Wat Arun falls into the category of "places where getting there is half the fun." Reaching this stunning riverside temple involves at least one and often two boat trips, during which you'll get good views of the city's skyline and closeups of life as it's lived on the Chao Phraya River.
Located in Thonburi, Wat Arun (literally "temple of dawn") looks quite different to other houses of worship in Thailand because much of it is decorated with leftover fragments of Chinese ceramics.
Be sure to climb as high as is allowed on the main monolith for views over the area. Be warned: The steps are steep, so take special care when coming down.
It is often visited together with Wat Pho, from where you can take a 3-baht ferry ride across the river. Wat Pho is served by the regular boats that sail north and south along the Chao Phraya.