The phrase Qian Men is actually a reference to two separate towers on the south side of the square which together formed the main entrance to the Tartar (or Inner) City. The southernmost Arrow Tower (Jian Lou) is no longer open to the public. You can, however, still climb up inside the rear building, called the Zhengyang Men, where an enjoyable photo exhibition depicts life in Beijing's pre-1949 markets, temples, and hutong.