As We All May Know The, Minecraft Scp Map "SIte-21" is Being Updated And Is Currently Not Downloadable. On Top Of That We Don't Know Whether The New Map Will Be An Extension Or A Complete Remake. So I Took it Upon Myself To Recreate The Classic "Site-21 Map". You Will Spawn in The Cafeteria, .This is a Work In Progress. I Will Be Posting Updates... (P.S You Can Explore The Facility Inside of the Main W.IP Building,)
Okay, sorry for the lack of updates but its done, well even though you cant download the real map yet, i found it in my one-drive this is the EXACT Replica
(my suggestions): allocate as much ram as you can to minecraft whilst at least leaving 1 Gigabyte of ram for windows to run, and turn your setting all the way down. use forge version. (forge-1.12.2-22.214.171.12468 (ps, use all the mods or else the map wont really be full. but you can remove modern warefare iyw.)
If you downloaded the map from the link on the original post then you should spawn with items in your inventory and you should be close to some stone hills, you can either go into spectator mode and go under and look for the site or you can just fly towards the big white building and find a way in.