The Endurium Floor is a floor you can build (the Endurium kit).
In-game description
Pale stone veined with endurium, polished smooth. On an upper story, also the ceiling below.SHOWN IN THE BUILD RING
Building it
It costs 1 
Stone, 1 
Endurium Ingot, 2 Earth spirits. It needs 4 Jewels first. Take it down with DISMANTLE to get its cost back (see Building).
