The Magic Mountain is a rear entry sex position. To get into this position, stack a pile of pillows one on top of the other and the receiving partner lies on them face down. The stack should be high enough that when leaning onto the pile, there is a natural arch in the back. The penetrating partner enters from behind and forms to the shape of the other partner with their chest on the back of the receiving partner and arms on the arms of the partner.
More About Magic Mountain Position
The Magic Mountain position allows for deep penetration at a different angle than other rear-entry positions. The pillows allow the receiving partner to be comfortable while leaning on their arms since the pillows provide a soft surface. It also allows for closeness between partners without being face-to-face.
You can also use home furniture or sex furniture to achieve a similar position if you don't have enough pillows available (or find that pillows are compressing too far under the weight).