The 24m-high That Chomsi, erected in 1804 and restored in 1914, stands at the summit, clearly visible from most ground-level points in the city. This stupa is the starting point for a colourful Lao New Year procession in mid-April. If you continue over the summit and start down the path on the other side, you'll come to a small cave shrine (sometimes called Wat Tham Phu Si, although without monks it's not officially a wat).