Rangoon Central Station. Guards or station employees will direct you to the crossover to Tracks 3 and 4. The crossover also gives access to Pansodan Street, which crosses the rail yards on a highway bridge. At the ticket office on the platform, we bought the 600 kyat (tɕaʔ) (= $1.00!) ticket for the "luxury" air-conditioned train. At the last minute, we took the non-air-conditioned train with open windows instead, which should have cost only 100 kyats (15 cents).
The Circle Train is great fun! Take it.
The Myanmar Times has an article on upgrading the Circle Line. The Irrawaddy describes the Japanese-built air-conditioned train (the one we did not try).
Photographs taken with a FujiFilm E-E1 digital camera with RAW files processed in PhotoNinja.