The starbounder wiki says the Glitch Castle can be found on any planet (which is true) but can found most often on volcanic worlds. Actually, it's found in grassland areas, similar to what you see on lush planets. On over twenty volcanic planets, only one had a Glitch Castle. The Glitch Evil Fortress and Glitch Dungeon Crawler was found in abundance, but the Glitch Castle, Glitch Village, and Old Sewers (which, I'm not sure, but I got the impression may be Glitch related?) are rarely found on the volcanic planets. I don't have an account on the wiki, as I'm not one to do much digging for information, but I just wanted to save someone else the headache of searching so many planets. I know the main quest says you can find the glitch there, but it must refer to those dungeons, or something. Grabbing the armed display armor was a giant pain because of this lol.