This is very loosely based on the burial mound symbol from Profantasy, and after watching several documentaries on such burial mounds.
generic burial mound, outside
generic burial mound, inside
1) entrance
2 thru 5) burial areas
6) ceremonial area
7) passageway
clicking on this thumbnail leads to a 769 × 768 png file of 33 Kilobytes.
40 feet in diameter mound