I'm not sure what triggered it but I have got the 'Wherein we Fortify' acheivement for building 100 upgrades. For the most part I play without upgrades at all since I can never decide what to build and I sort of forget in the end. Essentially, I have built maybe 10-20 upgrades total over the course of all my games combined. No where near 100.

Could this achievement be bugged at all or are other things counted as 'upgrades' that might be less obvious to me? Or is my counting so completely off and I really have somehow built 100 buildings?