I know I said I'd only be doing this once a week... and a well is kind of a lame feature (anybody could make one.) But I needed some practice to make sure I was able to duplicate the style of the first geomorph, plus I needed modeling practice, since some of the S-series geomorphs I have planned are going to need fancier models.
So, here's a well in a cave. Floor of the cave is sunken compared to other areas of the geomorph. You could add a secret door to the curved tunnel in the east that leads to the triangular room, although unless you add a ladder or staircase, it will be a short drop. Or, you could add a narrow slit so that explorers in the tunnel could get a vague glimpse of the space beyond; they will need to navigate through at least three geomorphs to reach the cave, though.
For the record, here's the well (and bucket) model from a different viewpoint. I suppose I should have made the bucket lie flat, but I render the models in Google Sketchup, and I have a lot of problems positioning things in Sketchup (one of the reasons I want practice.) The model itself I made with Wings 3d, and I assemble the geomorph in Inkscape.