Colossus

Giant stone monolith overgrown with moss and other plant life.

Its belly is a reservoir of fresh water, protected by some sort of magically strong crystal.
It drains over time from the plants it hosts, so it must eventually seek sources of water to refill itself.
It languidly roams around the area near a vine enwrapped entrance to a ancient stone temple.
While mostly peaceful, it becomes instantly aggressive to any who come too close to that entrance.
Sometimes bothered by a tiny creature, with very impressive climbing grip strength, shining light at it with a sword.