The very old temple of Wat Visoun, also called Wat Wisunalat is built on the south side of Phou Si hill, outside of the main area of the old city. The temple's most notable feature is the large squat stupa in its forecourt. The stupa is properly know as That Pathum (Lotus Stupa) but is more commonly known as That Makmo because its shape resembles a watermelon ('makmo' being Lao for watermelon).
The stupa was originally constructed around the turn of the sixteenth century. Its interior was originally filled with hundreds of small Buddha images fashioned in precious metals and crystal. When the Chinese Haw sacked the city's temples near the end of the nineteenth century, the smashed open the stupa and stole most of the images. What remained is now on display in the Royal Palace Museum.
Inside the large sim is a typical alter with the typical large seated Buddha image surrounded by many standing images. In addition to these, around the outer wall of the sim behind the alter are arrayed many more standing Buddha images (a pose commonly refered to as the 'Calling for Rain' style). These were moved here from other destroyed temples after the Haw invasion.
The temple is adjacent to Wat Aham, so a visit to one typically takes in the other.