Four corners of the Earth
Connect Tempelhof, Alexanderplatz, Schloss Charlottenburg and Potsdamer Platz. If you're like me and know nothing of the world and its wonders - those are in Berlin.

These locations are all fairly large plots of land but are also unassuming - except for the Schloss Charlottenburg which is a castle in the middle of empty plazas.

This achievement reportedly has a bug - it has to be done in Sandbox.

Fortunately if you start a Sandbox game on easy you'll have enough money to build four helipads and buy either helicopter with a little cash left over.