The Pergamon Museum was the museum that I really, really, really, really wanted to see while I was in Berlin.
To start with, the Pergamon Museum is located on Museum Island, which is awesome. An island made up of museums? Sounds fun to me. (And yes, it actually does sound fun to me – stop judging.)

Also, it’s used to house buildings. Yeah, that’s right – buildings. They’ve recreated buildings and facades in this museum, moving the pieces from the original location into here. One example is the Pergamon Altar, from the ancient city of Pergamon (and the reason behind the name of the museum).

Nobody really knows what the purpose of this Altar was. The long-time director of excavations in Pergamon, Wolfgang Radt, was quoted saying: “No research is undisputed concerning this most famous artistic masterpiece of Pergamon, neither the builder nor the date nor the occasion nor the purpose of the construction.” (Wikipedia)
Mysterious, eh?
Personally the artwork in the friezes is definitely worth a look. The Gigantomachy frieze shows the gods struggling against Gaia; there are gods, animals, fighting… it’s almost like a HBO series.
What I really wanted to see, though, was the Ishtar Gate:

I first learned about this gate in Art History class (way back when), and I’ve always loved the look of the blue stones. It was constructed by King Nebuchadnezzar II as the 8th gate to Babylon, and there’s a (completely unreadable) inscription by him on the left side. The gate was once considered one of the Seven Wonders of the World, until that damn lighthouse bumped it off the list…
It’s something that you have to look at up close – the blue bricks, the animals (which are not flat against the wall but rise out from the bricks), the inscription, the blue bricks…

There are lots of other interesting things to see at the Pergamon Museum, but I definitely recommend spending some up-close time at the gates.