This is map specific and you must be playing on Father Campbell's Chapel. It's a variation of the Asylum map.
You are not required to buy the DLC or own either of the new characters to get this.
https://c-8oqtgrjgwu46x24f3w7r5n6yrca5mx2eenqwfhtqpvx2epgv.g...Simply activate the generator which should be located on the second floor of the inside of the church and then escape.
This is however more difficult than the other map related achievements as this map is on the smaller side. Factor in that the church takes up most of the map and the inside of the church is also very open with not many places to hide.
Like all the previous achievements, you don't need to do the whole thing by yourself, just be on it when it finishes. So you can rush it just to make sure someone else does it or you can wait back until you know the killer is preoccupied and then go in.
As for getting this map that's a different matter entirely. I was purely joining and quitting just to get this map and I got it about three times over roughly ten hours.
Currently no specific offering exists to get this variant but you can use either the brown or yellow rarity Lunacy Tickets or the green (which should guarantee unless someone else uses a map based offering) Wedding Photograph, all three are supposed to bring you to the Asylum but then you have a fifty-fifty chance of getting the Disturbed Ward which is the old variant or the one you actually want which is Father Campbell's Chapel.