My Time At Portia

While in the Abandoned Ruins, you will sometimes come across pipes that lead to hidden areas. These are totally random, but do show up as purple orbs when using the Relic Goggles you get when in the Ruins .

I found this when I was in #2, near the bottom. Although it is totally random, so best bet is to just explore the ruins normally, and I'm sure you'll eventually manage to come across one naturally.

When your in the Ruins you can sometimes see purple points. These are abandoned rooms and when you dig your way towards it and enter it, you'll unlock the achievement. Check the video if you need more details, thanks!