Is tennis shoes a must wear. We forgot ours at home

I would say yes to be on the safe side, but more like closed toe shoes and rubber sole.

I agree with others that say anything with a rubber sole should be fine.

Its not a must but its recommended

I wore my water shoes, as long as you have shoes with good grip you should be fine.

It's easy to slip in the caves so shoes with good traction is a must.

No you should be okay without them. The caverns are wet. Anything you have with a rubber sole would be great. Really impressive to see them. Definitely worth the effort.