Just got word from a group of professional Thai tour guides that the main prangs at Bangkok's Wat Arun will be closing to visitors starting Sept. 24 due to a large scale restoration. Apparently the giant brick base is 'eroding', and there are concerns that the prang could eventually topple if nothing if done. This is a major undertaking -- they're saying up to three years before it reopens. Visitors will still be able to peep the prangs from a distance; they just can't climb up them. The ubosot and other buildings should remain open.
So... If you're keen on climbing one of Bangkok's best known landmarks, you'd better do it soon.