Open depending on the weather. When it snows, it is best to stay down, because the mountain spirits here love the sun but not snow. Bring water and something to eat. From Na Ngua it is also a feasible excursion with children who can ride a bike.
Upstairs there is seating and a lot of things to see. I like to climb there myself. You can listen to the wind up there and see and hear birds, ants, crickets and bats. Depending on your patience.
If you're lucky, you might even run into a flying squirrel or, if you like bats, big ones
Families of them in the cave system. Ask the monks, they'll be happy to show you where they live. See also another report on this mudflat, with travel routes information