The Dwarfie Stane, Orkney. A sandstone monolith with carved interior chambers, a tiny door aligned exactly west, and a plug that fits snug yet allows a little air inside. The chamber has a sonic resonance near identical to that of the box in the Kings Chamber at Giza.
The earliest Vikings found the monolith sealed with no one inside, and by their time no one knew who carved this or why. The design is alien to Britain, its roots lie in Domus the Jannas Salixi (Chamber of Faeries) in Sardinia, whose chambers were cut exactly in the same shape and manner, with an identical sonic fingerprint. This resonant frequency of 116 Hz acts like a switch between the brain’s hemispheres to facilitate an alternate state of awareness. Curiously, both sites were associated with initiatory rites, and folklore describing their creation by very very tall people.