The 5,000-year-old burial site in the Orkney Islands came to light when a homeowner dug away a small mound in his yard to improve his ocean view, National Geographic News reported.
A camera lowered into a crack between stone slabs making up the tomb's ceiling revealed a prehistoric skull sitting on a pile of muddy bones.
"Nobody had known it was an archaeological site before that," Julie Gibson, county archaeologist for Orkney, said.
"We have got the assorted remains of many, many people who have been deposited in this tomb at different times," she said.
About a thousand skeleton parts belonging to a mix of genders and age groups, including infants, have been unearthed so far.
Dubbed the Banks Tomb, it's the first undisturbed Neolithic burial site to be discovered in Scotland in 30 years, Gibson said.
The site was first named the Tomb of the Otters when initial excavations revealed prehistoric otter bones among human remains.
The animal bones suggest people visited the burial site only sporadically, Gibson said.
"It suggests the tomb was not entirely sealed and that otters were trampling in and out a lot" throughout the tomb's use, she said.