Additionally, are there any other interesting things on the planet surface besides just the entrances to the cities and caves? I recall mainly just using the surface as a place to level up by fighting nasty creatures. Are there any other interesting things up there, like some Easter eggs perhaps?
Mars Saga was polished up and re-released a year later on the PC titled Mines of Titan
There were a few plot changes but the city maps remained the same.
Here's a link to the original Mines of Titan manual which contains maps of the cities. It's been scanned into a pdf. I don't know how useful they'll be but it's better than nothing.