Underwater ?

Some kind of underwater caves like … this one ? http://en.wikipedia.org/wiki/Cosquer_Cave

I have no idea to get there, though.
Through long and windng roads … tunnels from the surface to thre ?
Or through a spell that makes one able to "breath" under water ?

Edit : Here is a picture : http://www.culture.gouv.fr/culture/a…/fr-cosqu1.htm