One of my favorite mod in Skylines that you can import _real world_ terrain maps into the game. Building your own city but better is a good fun (and challenge!) https://terrain.party/ Hope this will work in the sequel too
It would be incredible to have a globe viewer/DEM download tool built in to the game, but the bandwith required for hosting the project might turn into an issue (I'm reminded of the situation with high res imagery for Command: Modern Operations/TacView, where users are strongly encouraged to download only what they need due to server constraints).
Use this instead: https://heightmap.skydark.pl/#