Fastest way to unlock a new map.
Easy Guide to Unlock New Map
This is also a little Easter egg from the producer : this map is a play location in Witch Hunt.
You need to find the Dream Pill and drink it to unlock the new map.
It may be distributed in how a place of the map, usually in a specific location with props, such as in a castle or some conspicuous place. You just need to keep looking for it and you will most likely find it.
For example: I found it upstairs near the strange tree.