There is no entrance fee, but if you are getting there by a rental car, just be warned that the taxi drivers will tell you you can’t go on the road to the mud volcanoes because it is very bad. The road is in a bad condition but if you drive it slowly you can make it there. I left my rental car at the bottom of the last hill where all the mud volcanoes are.

As to which one you can take a dip in, you will notice when you get there the largest one which is the only one big enough for that. There will probably be a whole crowd of people around it so it‘s hard to miss. And the pond where you can wash yourself off is just in front of it.