Pakse is the transport hub of the region, with an airport, bus service and limited boat access off the Mekong. For Champasak and the South, there are minivans (110,000 kip return to Si Pan Don) bookable from most hotels and tour agents in Pakse town centre. These are nearly always packed with irritating 20 somethings usually wearing Beer Loa singlets and spotting scars from scooter accidents, also don't expect any leg room.
From Pakse southern bus station, take a songthaew (starting 9am until 11 am; could be very crowded, 20,000 Kip) to Champasak (~2h) or Than bhan khop (2h15), near the crossing to Wat Phu. In the latter case, you have about 30min walk to Wat Phu entrance.
Motorbike - rent a motorbike in Pakse, head south and cross the Mekong via the Lao-Nippon friendship bridge. After 1.5kms, take a left turn onto a new, excellent condition and quiet road which goes directly to Champasak. It's a scenic ride between the Mekong and Karst formations. You can drive up the road to Wat Phu and stop to taste the various foods the street vendors sell, for foreign traveller with no Laos language skills, it going to be point and hope as little to no English spoken.
Wat Phu (Vat Phou). A c. 12th century Hindu temple built in the days of the Khmer Empire in the style of Angkor. The temple is still in use as a Buddhist site. The park is only open during certain hours (such as 9am to 4:30 pm.). 50,000 Kip for temple and museum and 15,000 for golf car (the entrance gate is far from the temple about 800 metres).
Wat Nang sida 2 km from Wat Phu on the ancient road to Angkor Wat. Big ruins with massive big stones under reconstruction.
Thao-Tao ruins of medium size temple 1km from the previous one, difficult access on dirt road and forest.
To Mo ruins on the other side of the Mekong.
Lingaparvata sacred mountain (1416mt.). The top has a natural stone lingam of 10mt which can be seen from the bottom of Wat Phu. Impossible to reach the top, maybe with 2-3 days trek.
All these sites have the status of UNESCO world heritage.
Champasak spa, ☎ 02056499739. 10am to 7pm. Clean place. Really good service. Professionnal. Nice view on the mekong. Differents types of massage (herbal - 95 000kip/1h, oil, feet massage, hair treatment). You can relax and take a tea in the garden.edit
Champasak with love. Sleep : This place is a restaurant, but now they offer room. (Open spring 2014) 45 000 kip for fan room. 85 000 kip for A/C room. Bicycle rental for 15 000kip. Bathrooms are really clean and rooms too. (Nice) music playing all day. Nice terrasse on the Mekong. The staff doesn't really speak english but they make efforts to be the most helpful possible.edit