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Taversöe Tuick (or Taversoe Tuick) is a Neolithic burial cairn on Rousay, Orkney, thought to date from between 4000 and 2500 BCE. The monument includes a rare example of a double-tiered chamber, an upper chamber approached via a passageway and a lower subterranean chamber, originally separate, which can now be reached via a modern ladder from the upper chamber. The monument includes a third miniature chamber slightly downhill of the lower chamber.
The site is a scheduled monument in the care of Historic Environment Scotland, and the monument and chambers are open to the public. (Wikipedia)

In the United Kingdom, a scheduled monument is a 'nationally important' archaeological site or historic building, given protection against unauthorised change.
There are about 20,000 scheduled monuments in England representing about 37,000 heritage assets. Of the tens of thousands of scheduled monuments in the UK, most are inconspicuous archaeological sites, but some are large ruins.
Wikipedia: Link