A small, crumbling ruin, the temple of Ak Yum lies just off the track along the southern embankment of the West Baray and was clearly heavily damaged during the lake’s construction.
An inscription from 613 AD has been found at the site, indicating that probably the first temple here dated to either the reign of the great Ishnarvarman himself or his father Mahendravarman, though it was during the later seventh, early eighth century and the reigns of Jayavarman I and his daughter Queen Jayadevi that the capital was moved to this site. Ak Yum more than likely became the state-temple of their city Aninditapura.
Though now all that can be seen is the remains of a laterite step platform surrounded by a few piles of bricks, it must have been a lot more impressive in its prime and was certainly the first ever step pyramid-type temple constructed by the Khmers. The sparse remains seen today presumably date from an upgrade during Jayavarman II’s occupation of the area. Note there are no guardians at this temple so probably no pass is needed.
It’s not worth going out of your way to find Ak Yum, but if you’re cycling around the baray it makes for interesting feature to pause at en route.