There are fairly interesting caves around Vang Vieng, but finding them can be a little tricky. There is also plenty of misdirection, several 'blue lagoons' have sprung up around the original blue lagoon. Now I'm old and less adventurous it's easier to use a smartphone, despite the fun I had with two other tourists searching through the undergrowth for hours. The trouble is, in Laos half of the roads haven't been added to Google maps, let alone tourist places. You end up scouring the satellite images for the winding yellow lines, with limited data.
Some local locations:
Tham Hoi & Tham Loup
(Possibly aka snail cave)
Tham Hoi is a pretty good adventure; pleasantly undeveloped and quiet, several kilometres of cave with glittering white deposits and an underground river. You can explore both up and downstream, but you sometimes have to swim which is a fairly unique experience underground. Sharp and slippy rocks though, fairly dangerous for the feet. Entry for both caves 10000 kip with torch. Apparently Tham Loup is also pretty deep, nearby and included. We cycled it's about 14km.
Tham Hoi entrance google maps
Tham nam (water cave)
Seems to be the location for underground tubing... Buried under crowds of people.
google maps tham nam
Pha Thao cave
North of vang vieng roughly 10 km. It's got a few big chambers and impressive stalactite galleries. One guide book suggests it is 3km but none of the side passages seem to lead anywhere after less than 200m. Quite quick in the end, 10000 kip, worth it perhaps en route to the others.
Google maps pha thao cave
'Python Cave' (I forget the Laos name)
If you're cycling or driving the loop in the valley on the west side of Vang Vieng, this cave is worth a stop. It's many hundred metres long, and takes an hour at good speed. Ignore the sign which says 'finish here' after the first hundred metres! Generally tall chambers, not too much stooping, but occasional other tourists which lessens the adventure. Entry 10000 kip with torch.
I think the location of python cave, Google maps
The rip off.
You don't know what you are spending your kip for until you get inside. Only a few metres of cave are easy, followed by a more dangerous stretch on a sloping surface. This didn't seem to go anywhere.
I think this is the location, on the route to the overcrowded blue lagoon.
possible Google maps
Blue lagoon, cave, zip line, crowds.
Search for the 8 parked minivans on Google maps, though this is out of date, expect more.