Bryn Celli Ddu is generally considered to be one of the finest passage tombs in Wales. Its passage and burial chamber are complete, and it is still buried under a mound or cairn, re-instated following its excavation in 1929. (Many stone chambered cairns have lost these features.) As it now stands, the passage is long, the first being unroofed with a pair of portal stones. The main passage has walls of vertical rock slabs, roofed by a series of stone lintels. The mound, being substantially smaller than as originally made, no longer completely encloses the burial chamber, so the back wall is open to the air, allowing some natural light in.