This is the St Albans map for the upcoming event: https://forums.taleworlds.com/index.php/topic,144741.0.html for the mod
Blood and Roses https://forums.taleworlds.com/index.php/board,195.0.html
It will most likely be included in the next update before the event or if not you will donwload it when (and if) you join the event so if you really want to try it out early then here is the terrain code:
0x00000001300389800003a4ea000058340000637a0000399b

If you don't know how to apply that then don't worry you will get it soon enough