Besides the imposing prang, Wat Arun of course also has a number of other important temple structures such as its Ubosoth (Ordination Hall), the Viharn, a gallery with Buddha Images around the Ubosoth, a bell tower, a mondop with Buddha's foot print, and two temple guardian figures in front of the Ubosoth.
The Ubosoth closes relatively early, around 4.30 P.M., so you would have to come on time if you want to have a look inside