I have tried setting both a lattice or rock to be a cave entrance, but during rendering these items come out black. Any suggestions?

Not sure what you mean, do you have any screen shots?

you'll need to set your terrain to be 'solid' before it'll correctly boolean w/ a rock or a lattice.  and rock and/or lattice probably also need to be set to solid.

for the rock, click the 'E' next to it and check the 'solid when boolean rendering'... for the terrain and/or the lattice, I forget exactly where the solid option is in the terrain editor, but I'm sure someone else here knows...

Oh I see, but then if the rock or lattice are rendering black it means there is no texture on the rock or lattice, so even if you boolean with it, the cut edges will render black. 

The best idea then is to have the same material on the rock or lattice as you have on the terrain you're trying to cut into.

For the lattice and for the terrain the 'set to solid' option is in the terrain editor, which you access by clicking on the E, and then on the little black arrow on the top right corner of the "terrain canvas".

Plus the terrain must be set to positive and the rock or lattice must be set to negative, then group.

Thank you Fran and Calyxa
These are some great ideas I'll be sure and put into action

I will say that while I was experimenting with booleaning a cave I did find it very hard to see inside the cave, once made.

So I put some water inside, and a light, this worked fine, but if going further with it, I'd have to think about using some rocks or another lattice to half block up the entrance, or the water looks odd.  As it was I tilted the water, to try and get it to look more natural - the other option is to first tilt the lattice you are using to do the booleaning.

If you look at this image and notice the line of the water's edge between the two red arrows? That's what I mean.  And that's after tilting the water.  Before, it was a lot worse.

Fascinating cave and lighting, when I get back to the Bethlehem cave I'll be sure and post it. One more question. When importing picture of the scene into Renderosity it limits the size. But when clicking on your scene it opens into another page with the .jpg. How is this accomplished?

It's automatic, Renderosity does it for you.

If you need to know how Renderosity does that, I suggest you ask in the 'Community Centre' forum.

Bethlehem Cave, huh?  Interesting.....