Remember this thing? It's a magic item and I had a thing in this blog about how we were all gonna write it up as a magic item.
I decided it was Forgetting Dust.
Forgetting Dust removes whatever it touches from the memories of men, women, and beasts.
The unusually high concentration pictured here is enough to not only cause the glass and vitrine to be forgotten, but to cause the location of the room it is in to be forgotten, to make mapping the building the room is in impossible, and to cause the location of the city in which that building, room and pile of dust lie to become permanently obscure to all travellers, despite the fact that it lies along a major trade route.
The room also contains a number of powerful and terrible devices as well as maps, pets, poems, poets, founding documents of various religious faiths, chemical formulae, musical scores, and dinner recipes that were all deliberately placed in the room (generally at great cost and with great difficulty) over the course of milennia by those who wished them forever forgotten.
Here are the rest of the write-ups...