Hi Brett. If you are concerned that the shadows look wrong, here's some thoughts on that:

Shadows require a light source, so unless you're planning to place some torches and other such objects in your map and then rendering that, I would just leave the ground area flat. Caves are usually very dark anyway, so realistically the shadow would be everywhere.

If you added those shadows to break the monotony of a flat rendering, there are better ways of doing that. Try this: find some free dirt or rock texture online, then duplicate your rock layer (the impassable terrain) and paste that texture onto it. Change the blending mode to multiply and adjust the opacity, so it's not too visible and distracting. Make sure to squish the texture vertically a bit as well, so it doesn't look out of place in the isometric setting. You can also click on the effects button at the bottom of the layers panel and play around with those, I'd suggest inner glow, but change the color to a grayish one and the blending mode to multiply. This effect will only work properly if your rock layer isn't a flat layer at the bottom. If it is, you can still do this by creating a new layer, selecting all the grey pixels with magic wand, and then hitting the layer mask button at the bottom of the layers panel. You can experiment with a bunch of different settings in the effects panel and maybe discover something you like. You can add another texture and other effects to the floor layer as well.

I would also play a bit with the size of the isometric grid here. It makes those narrow passages look extremely narrow and kind of awkward, especially if you imagine one square to be roughly the size of a person, though I can't assume this was the intent, I'm only guessing. Try how it looks without the grid too; I think the stairs would look better, because the height level changes, but the grid stays flat everywhere, so they're interfering with each other a bit.

I hope you found something useful here. I like how you have three ladders next to each other in one place, because it makes me wonder why, and my imagination tells me some crazy things.