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When the coronation of a Luang Prabang king was pending, he spent three days in retreat at Wat Longkhun before ascending the throne. The central sǐm (ordination hall) features old murals, one of which depicts giant fish attacking shipwrecked sailors. Ask at the ticket desk for the key required to visit Tham Sakkalin, a humid, slippery 100m-long limestone cave. It's a three-minute walk further east then up a few stairs. A few Buddha fragments are kept here. Bring your own torch (flashlight).