Phong Nha-Ke Bang
Phong Nha has now become well known as one of the most beautiful and interesting areas of Vietnam. Tourism in the area is booming, and the choice of transport, eateries, accommodation and tours improves all the time. Coming to Phong Nha really does provide a chance to get out in the real Vietnam on a bicycle or walking and soak it up.
The Phong Nha Farmstay in 8km south of Phong Nha, deep in the Vietnamese countryside overlooking rice paddies, and is situated to easily explore the area.
Currently, the closest service is via Vietnam Airlines to Dong Hoi, check their website for latest fares and flight times.
Several arrivals and departures at Dong Hoi daily from as far away as Hanoi and Ho Chi Minh City, only a few hours from Hue.
Local yellow-green buses from Dong Hoi cost 33.000 VND (Jun 2015, they give you a ticket) and take ~1h 15min. The road is a bit bumpy, but the bus has AC. In Dong Hoi, the bus has a stop in front of Nam Ly bus station (which is in front of the train station across the small pond - you can easily find it on Google Maps, but it's not on the latest version of maps.me), at To Huu street. It then goes north with more stops along Huu Nghi street. Ask at the information desk at the bus station, as there isn't a bus schedule you can check. I was told the bus was at 17:00, then on second thought at 16:30, and in the end it came at 16:25, so better pay attention and be ready in advance. They will ask you where to be dropped in Phong Nha. There's a stop just in front of Easy Tiger.
Many companies now offer motorbike/scooter rental in Phong Nha. When choosing a rental company you should take in to consideration the cost, maintenance of the motorbike, quality of the helmet supplied and breakdown/rescue services in case you have a problem. It is recommended that you spend a couple of dollars more to get a good motorbike from a reputable rental rather than getting the cheapest motorbike.
The National Park has some spectacular caves an scenery, but the roads are narrow and winding in places. Please ensure that you have sufficient riding experience to take on the remote landscape of the park before renting a motorbike.
If you do not have experience riding a motorbike, you can arrange for an easy rider from the Easy Tiger Hostel. This provides employment for local people, a safe licenced driver who knows his way around, and gives you the opportunity to enjoy the scenery more than if you were driving and navigating for yourself.
Motorbikes can also be rented for 150,000 to 250,000VND from hotels in Dong Hoi. It takes about 1 hour via the Ho Chi Minh highway. The Phong Nha cave is about 45 km from Dong Hoi and the Thien Duong (Paradise) Cave is about 70 km from Don Hoi.
Pickups from Airport, Train Station, or Tourist and Local Buses to and from Ha Noi can be arranged for around 500,000VND through the reputable hotels and accommodations in Son Trach (Phong Nha) and Cu Nam.
Taxis can be hired from hotels/resorts, airport or train station in Dong Hoi. About 1 hour on the Ho Chi Minh highway with cars, oxcarts, motorbikes, buses, trucks.
Tours are available from both Easy Tiger Hostel at Phong Nha and Phong Nha Farmstay in Cu Nam.
Hotels in Dong Hoi can arrange day trips to the park but best to stay in Phong Nha as Dong Hoi is 50km away.
The National Park was opened to the public in 2010 and consists of pristine untouched jungle spread throughout a rugged landscape. The area is full of large cave systems, the most famous being the Son Doong, Paradise Cave, Hang En and Phong Nha Cave. An 2013 it was announced that tours to the largest cave in the world, Hang Son Doong, would be opened to tourism in 2014. Oxalis Adventure Tours ran pilot tours in August 2013, and commenced operations in January 2014 with a six day exploration costing 3000USD per person. In 2015 the tour was reduced to 5 days in the caves but the price was retained at 3000USD per person.
The Phong Nha Ke Bang National Park is not very 'open' as yet. The area is close to the Laos Border, the military has a presence within the park, and the park has one of the highest concentrations of unexploded ordinance (bombs) in the world. Currently, you are not allowed to hike or trek through the park without a licensed tour operator, and most of the hiking is found as part of caving expeditions, such as to Hang En. There are 2 roads that travel through the park, the Ho Chi Minh West Highway, and Highway 20 (otherwise known as 'Victory Road'), and these create a loop which can be travelled by motorbike or on a tour.
Phong Nha and Tien Son Caves: As of January 1st 2015 prices have nearly doubled It costs 150,000 VND to visit the Phong Nha cave and 80,000 VND to visit the Tien Son cave and 320,000 VND to rent a boat for up to 14 people to visit one or 350,000 for both. You can share a boat with other tourists that show up. Renting a boat is a requirement as there is no other way to get to the caves. Caves are exquisite and very large. It is about 45 km by road from Dong Hoi and takes about an hour by motorbike. Or call direction to Phong Nha tourism (tourism manage organization) to book the ticket: 
Nuoc Mooc Spring Eco Trail: 80,000 VND for ticket (March 2015). Transportation can be negotiated to take you there from Phong Nha village. Buy ticket at the hut under the sign off the road, then wander the bamboo bridges and paths along both sides of the river/rapids. Go back to see where the river springs up out of the ground. This is also on the road to the Thien Duong (Paradise) Cave.
Thien Duong (Paradise) Cave: Newly paved road off the main HCM Highway provides car/motorbike/bus access. Buy 250,000 VND (March 2015) ticket to enter; the fee includes an English speaking guide. Just after that, separate >>optional<< ticket for non-polluting electric golf cart to the base of the stairs (if nice weather, walk along the new path of about 1.6 km instead). Approx. 500 stairs up to entrance of cave, another 100-200 stairs down inside. Stunning, tastefully lit cave features along 1.1 km of new (spring 2011) wooden pathways. It is about 70 km by road from Dong Hoi and takes about an hour and a half by motorbike, or around 30 minutes if you are staying in Phong Nha. Some claim that this is among the most beautiful caves in the world.
Tu Lan Cave System, (About 40km from Phong Nha). One of the most beautiful untouched areas of Vietnam showcasing minority cultures amongst real jungle, rivers and waterfalls. There are currently 10 known caves in Tu Lan sitting untouched for thousands of years. A special permit is required to visit this area which is only available through local responsible tourism operator - Oxalis Caving Tours. This area is ripe for exploring with plenty of underground rivers and waterfalls! Tu Lan is the Ha Long Bay of Central Vietnam hidden amongst the mountains! edit
Hang En is of the largest and most beautiful caves in the world, this is close to Hang Son Doong (the world's biggest cave). To see this cave involves a day trek through beautiful jungle and valleys, and through a minority village, and then an overnight stay in the cave. Tours can be arranged at Easy Tiger in Son Trach or Phong Nha Farmstay in Cu Nam.
Hang Son Doong is the world's biggest cave, discovered as recently as 2009. A cave so big that a whole Manhattan city block, skyscrapers and all, could fit inside of it. Tours started in 2014 and numbers are restricted to only 10 tourists/week during the caving season from February to late August.
Bicycling and kayaking, trekking, camping and swimming at allowed points along the rivers.
The best way to see the National Park is on a tour, as you get a lot of information from experienced guides. The Phong Nha Farmstay National Park Tour is the original and best, but there are now some cheaper options which aren't as good.
The Phong Nha - Ke Bang Tourism Center has tours to visit the caves that are similar to the ones offered by Farmstay, but cheaper if you go on a group. However, joining an existent group won't get you a discount. You can book them online or directly at the center, at the bend in the main road of Phong Nha, next to the market.
Dark Cave 350.000 VND. Cave that you explore with headlamps, as it's not illuminated, whose main attraction is to be filled with mud. You follow a narrow passageway that leads to a mud pool, where you can lay down without sinking. It's silly, but fun. You zipline to the entrance of the cave, then return kayaking, and do a zipline jump into the river. They have lockers at the entrance, so you can leave all your clothes there and go into the cave just in your swimsuit.
With the souvenir shop at Phong Nha tourism center, the guest can get handicrafts, brocades, stones, bead products, bamboo and rattan products (rattan baskets, traditional conical hat ...), seafood (dried shrimp, dried squid, dried fish) Herbs, wide Honey. And local market is located front of the Center for guest have the time to walking visiting.
Thien Duong Cave: Along with the new road, several restaurants -- at the site entrance, as well as at the top of the 500 stairs! -- were being built for visitors in Spring 2011.
In Dong Hoi, there is a range of hotels/guesthouses, as well as at least one beach resort. About 1 hour travel time from Dong Hoi to the park.
At least two idyllic options very close to the park:
In Phong Nha Town near the cave boat dock there are several budget level guesthouses along the road TL20 (intersection with the giant sign that says Phong Nha Ka Be National Park) for around 150,000 dong or more.
Check park regulations first, or go with an organized tour. Park rangers are very suspicious of undocumented visitors overnighting in the park.
Be cautious driving on the road to/from Dong Hoi; avoid night driving.
Bring mosquito repellent.
By Motorbike: If the weather is good (and only then!) do consider the route to Khe Sanh. It is a 230km ride along the Ho Chi Minh Highway with the most stunning views and almost no traffic. Be aware that there is almost nothing in between. The first place to buy Gas is at Kilometer 82 and it comes with a very steep price (40000 Dong per liter). You will probably get to Khe Sanh on a full tank with a Honda Win but don't gamble. There are some smaller pubs and places to eat along the road but especially if the weather is warm make sure you have enough water with you. Also be aware that the weather can easily change, that you will take a lot of time, especially as you will feel the need to stop every few kilometers to shoot photos. So leave early and don't push it too hard. There are some places to stay in Khe Sanh.
Local bus to Dong Hoi departs at 5:30 am, and hourly from 6:00 to 17:00 except 12:00. Several stops along Phong Nha main road, marked with a blue sign. 33.000 VND (they give you a ticket)