The freeware game "Mobility" (at least I think it was freeware) had a very relaxing soundtrack, like many other city-building games do. The only YouTube video I can find is this gameplay video, but since the game has no other sounds beside the music going on, it'll work just fine.
I encourage you to listen from 3:33 onwards since the first part of the first track has a bit of a shrill trumpet like noise going on. The rest is a much more relaxing downbeat track. Another track starts at around 5:00 which is nice too.