By hire private vehicle
From Medan: For a bus to Berastagi go to Jalan Ginting, Padang Bulan Medan. A taxi from the city center takes about 30 minutes and costs 35.000 Rp. From here take the bus company "Sumatera Transport". The drive to Berastagi takes between 1.5 and 2 hours and costs 10.000 Rp per person.
From Parapat: At the pier for ferries going to Tuk Tuk there is a booking agent. From here you can go to Berastagi every hour ( 7am - 7 pm) with mini busses. The price 120 000.
Buses service many of the surrounding villages as is the case in the rest of Indonesia. Prices are similar to those elsewhere in Indonesia. Many run along the main road all the time. Central market is main stop.
Sibayak, Sinabung mountains, Sipiso-piso Falls, Traditional Karonese House at Lingga Village, Lake Toba (Tongging).
The tourist info is very helpful, it's at the top of the main drag by the fruit market. However, booking trips may be cheaper with local agencies, for example Losmen Sibayak Guesthouse (in the centre, next to BRI bank).
A climb of Gunung Sibayak is a must. A guide is not required but the path could be very slippery after rain, steep and confusing in some areas. Catch a minivan from the town to the bottom of the mountain. (Rp 3000)or walk it up from the town (around 40 minutes, nothing interesting on the way up). You could be asked to pay a fee of Rp 4,000 at the begining of the trek. The walk starts off by ascending a road paved the entire way up. When you reach "white rocks" on the left of the way, climb there and follow a narrow path, soon you'll find some stairs on the way up. It is a tough walk and water and snacks are a must, but those a basic level of fitness should be able to complete this with rests along the way. Don't go alone, wear good shoes. Three hours from start to summit.
The crater of Gunung Sibayak is filled with rocks that tourists have inevitably made into all sorts of shapes and words. From here, a good way to descend the mountain is to head off over the far side of the crater (3 o clock) down some very slippery surfaces. Beware though, there are some who have ended up getting seriously lost. In particular, avoid the trail that heads behind the antenna hill; you want to be heading down the opposite direction. Be extra cautious in foggy weather. Alternatively, easier and safer, walk back the same way you came and about 25? minutes from the summit a road veers off to the left (if going downhill). This will bring you to Semangat Gunung, the hot springs village.(1 hour?) From here, transport back to Berastagi is as easy as jumping on the first bus seen, not very often and last one around 6pm.
You can also go to Gunung Sinabung, the easiest way is to take a minibus to Danau Kawar (a lake at the foot of the volcano) and then hike up (you should ask for directions as the beginning is not obvious). After the initial pass through the farms the path is impossible to miss (although the usual stories about lost/dead tourists exist and are listed at the tourist information office in Berestagi), so no guide should be necessary. Good views from the top (weather permiting)and excellent walk through the jungle (the walk up to Sibayak is not quite so pleasan). 10 hrs hike.
Try betelnuts from the market. You buy the leaves, a paste, tobacco and a red nut. All are mixed on the leaf, rolled and chewed. The paste is lime so it has a kick to it.
Chinese restaurant in the main street has some good eating options and hot food. Food streets are opened along the side of main street after dark. Many type of Indonesian foods are available, mostly 'Ikan Bakar' (Grilled Fish).
For an adventure try the local specialty called babi panggang. It's pork meat in a special sauce.
Try the palm wine known as tuak at a local tuak house. Don't be surprised if someone breaks out a kecapi and starts singing. You can also snack on snake, monitor lizard, and dog meat.
Public transport to Lake Toba is possible and quite easy, however it is involving 3 minivan changes. First you need to go to Kabanjahe (20 minutes, 4000 IDR), from Kabanjahe to Siantar (3 hours, 20000 IDR, tell driver to stop at Sinpong dua) and from Siantar to Parapat ( 10000 IDR big bus, 20000 IDR minivan, around 1 hour, all prices as of July 2013). It is not so difficult as it sounds, it took us 5 hours (actually we arrived earlier than turists who used private transport ) and we waited no more than 5 minutes between changes.
You can also charter a taxi/minivan from the guesthouse and get there in 4 hours than whole day or Transporter for 450,000 IDR (Private Van)with their tour packages and transport price,see at their sites.You could also stop at the waterfall on the way ; Bukit Lawang seems to be best reached via Medan.
Minibuses to Kutacane (for Ketambe) come through from Medan; wait up by the tourist office rather than near the market as the latter charges 10,000rp extra (presumably some kind of commission). 40,000rp (Oct 2008), 5 hours through very nice scenery.