It's a bit like the icing on the cake of this 10.30 patch from Fortnite. The Prison is back west of Moisty Palms — a new rift zone.
The building is a new addition to the desert biome with its four watchtowers, its basketball court, and its many cells. There will be many chests and loots there if you are looking hard enough.
During Season 4 — in May 2018 to be precise — the Prison was partially destroyed by a meteorite crash. A huge crater had then damaged the building. You will notice that here, the Prison is back in its original version! Rather logical if we consider the Season 10 theme: time travel.