interesting. You can visit a similar cave system with an underground river (and go on a boat ride) in Czech Republic https://en.m.wikipedia.org/wiki/Punkva_Cave

interesting. You can visit a similar cave system with an underground river (and go on a boat ride) in Czech Republic https://en.m.wikipedia.org/wiki/Punkva_Caves https://en.m.wikipedia.org/wiki/Punkva_Caves