I love postcards with sites like these, sites that can just leave you in awe knowing that they really do exist.
This postcard is of the Cromlech Pentre Ifan in Wales. It is believed to have been a communal burial dating back to 3,500 B.C.
When I saw the stamp I had an immediate flashback of being 7 years old in front of the TV watching Thomas and Friends. Thank you Anu!