Between Old Bagan and Nyaung U is the Hitlominlo Temple, one of the last of the golden-era temples built before Kublai Khan's forces over-ran the city in 1287. The temple was built in 1211 by King Nantaungmya.
Although it is mostly exposed red brick today, the temple appears to have once been covered in plaster. The temple is designed in a style that some refer to as a "temple on top of a temple" due to the two level configuration. The square base is pierced by large openings on each of its four sides, and this configuration is repeated in a slightly smaller scale on the second level.
Within each of the four deep niches is a seated Buddha image. The niches are connected by an inner corridor lined with murals. The temple is a popular stop on the tourist trail, so the area inside and out is filled with souvenir stalls.
Note: Like all temples in Myanmar, you must remove your shoes and socks before entering the temple compound. Your best bet is to wear a simple pair of sandles, as the Burmese do. Generally, it's considered "bad form" to carry your shoes into the temple. Lockers are often provided at the more popular temples.