Assertion: tetrahedron | /r/HasProperty | walkable steel structure
Facets:
Source sentences:
text: The Tetrahedron in Bottrop (German: Bottrop Tetraeder or officially Haldenereignis Emscherblick) is a walkable steel structure in the form of a tetrahedron with a side length of 60m, resting on four 9m tall concrete pillars.