The Obelisk of Theodosius was originally a part of the temple of Karnak in Egypt, but Constantius II had it shipped over in order to commemorate his 20 years on the throne. It has inscriptions on it and some bas reliefs which are interesting. It is one of the few things that are left on the original hippodrome.
The obelisk is nice, but not very different from other obelisks. But I like the Hippodrom, with it's flowers everywhere and the nice atmosphere.