Mysterious Building Glitch?

What happened was that I was going back to my house since I was being attacked by monsters. But Then, out in the distance close to the jungle, I saw some unloaded chunks. But behind them I saw a building made of stone, Iron, Gold and some other blocks! I went up to it and when I went on top of it it was solid and I didn't fall down. then there was a hole that I went down but inside was not loaded so I saw other buildings like crafting benches surrounded by stone slabs but i wanted to explore it so I exited the game and logged on again. but it was not there! Sadly my screenshot button was broken so I could not take a picture