Puna Pau is the small volcanic crater that supplied the red scoria used for many of Rapa Nui's pukao, the cylindrical topknots placed on moai. Seeing the quarry helps make sense of the statues as an island-wide effort rather than a series of isolated platforms.
The site is quiet compared with the famous ahu, but the scattered unfinished pukao are exactly why it matters. They show the work in progress: stone selected, shaped, moved, and sometimes abandoned before reaching the coast.