The trojan barracks

The Trojan Barracks is a sneak strategy that on some maps can seriously damage your opponent. The concept is, that if you as Terran start close to anouther opponent, like on the Metalopolis map, you just might be able to fly your barracks to an unseen spot within the opponent base, quickly pump out a handful of marines (i like 5) and do a probe raid with them. This way you can raid the opponents probes again and again until your barracks is found.

In some maps, like Metalopolis, there is a hidden spot on the starting points. In Metalopolis its hidden nehind steam, but this could be trees etc. While it is still very close to your opponent, it is not visible unless you are behind the curtain. Thus, your marines can jump out like a cat from a box.