Landing Castles are vehicles that feature in Aldnoah.Zero.
By the current day, there were 37 Landing Castles that were in service to the Vers Empire that orbited Earth.
During the second invasion, at least 20 castles had descended to Earth's surface.
Each Castle was roughly 2 kilomters in length and could serve both as a stationary structure on a planetary surface or as a space going vessel.
Whilst space farring, they were designed to drop from orbit and crash into a planets surface to embed themselves on a world. This served as a useful military tool as it allowed rapid strike and eliminated enemy forces in the landing site.