This Pso'Xja tower is uncapped. Follow the path forward until you find a stone door, which, when checked, spawns an NMGolem named Nunyunuwi.
This NM has approximately 3500 HP, though offset by an innate Auto Regen trait that restores 100 HP per tick. If improperly handled, this effect can draw the battle out indefinitely. As a result, Nunyunuwi is often defeated with as much damage in as short a period as possible. Among the methods known (or theorized to be) effective are: