[Known] Fall through stairs and certain types of wood.

A non PVP example is in Central Britt where an NPC (Tarassa Rohandas) and players fall though the stairs and floor in location Area: Central Brittany (Novia_R3_City_Brittany) Loc: (390.5, 26.4, 292.1). The NPC falls continuously when trying to reach the bed to sleep.

I also found this is in the Rhun Ruins getting the "page of cruelty". I wont spoil the puzzle but its on the way to the switch to open the door.

Spoiler: Location

At the Base of the tower you stand on the steam vent and jump. It blows you skyward and you land near the coords I posted. As you try to walk up the stairs you will fall through. I found you can simply speed jump over the wall and complete the quest in its current state but the stairs used to work.

Rhun Ruins (novia_R5_Forest01_Rhun) Loc: (-179.7, 123.8, 54.9)

 

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Is the house in Rhun Ruins the same type of building? If not, can you put the location behind a Spoiler? Insert button ---> Spoiler