I can tell you by studying the video that the ground surface is made of back fill,most of the property on top has been dug out and returned, its like a heavy construction site that got the barest grading done. the retaining walls show the main boundary's of the main underground structure. the buildings are just decorations ignore them! its whats underneath that's impressive. did you see the dump truck it has its own special spot? below ground fuel tanks nearby and a small workshop/shed for equipment. as for the earthbermed court,it matches an anti-aircraft weapons emplacement,good spot on the island for all around security. the height is 6-8 feet like a hummer mounted stinger anti-aircraft system and i quote"
The Avenger Air Defense System, designated AN/TWQ-1 under the Joint Electronics Type Designation System, is an American self-propelled surface-to-air missile system which provides mobile, short-range air defense protection for ground units against cruise missiles, unmanned aerial vehicles, low-flying fixed-wing aircraft, and helicopters."
its size is as follows"
Length 16 ft 3 in (4.95 m)
Width 7 ft 2 in (2.18 m)
Height 8 ft 8 in (2.64 m) "

I have a background in hard-rock mining and military science. its really weird to have a fortified bunker complex next to a mansion
there's way more going on under that island than meets the eye....