A very easy way of getting this achievment is by launching the game with " --enable-dev-ui " in Steam launcher (Right click on game in your steam Library > Properties > Set Launch Options > paste " --enable-dev-ui ") and the Achieve it mod (Subscribe at the Steam Workshop to have it downloaded automatically and enable it from Skylines Main Menu under Content manager > Mods). When enabled you should be able to load up a map, select tab and unlock all buildings (I am not sure but i reccomend havng a city with more than 5000 people). Then save your game, close the game and steam. Then reload without the Dev UI options and load your saved map. The achievment should pop up and if not check that you have everysingle building unlocked (like bus stops and all types of transportation stops)