Just to clarify, Skocjan Cave does not have carts you ride in; it's all walking.
I assume raymonelee is talking about other caves they toured.
Note that photography is not allowed during the Skocjan Cave tour. You're
on some walkways pretty high up from the river below and it's fairly dark.
I can only assume there are a few phones and cameras down in the canyon...
Postojna Cave allows photography, is much more brightly lit, and has a much
more developed tourist infrastructure around it. But you do access the walking
tour with a small train that takes you in & out of the cave. Also, the caves are
accessible via local bus from downtown Ljubljana, so for that one you don't
really need a tour guide other than the one who takes you through the cave
as part of the standard admission.