Capsule hotels have been "topic du jour" for foreign journalists since at least the 1980s. It's time for them to get a new story. (But I hear that's hard because their editors in London and New York still want to see capsule hotels and people squishing commuters into trains for Japan ... and blue worker suits on bicycles for China).

If you want to see the building that marks the start of the "capsule" or "modular" building concept, then you could visit the Nakagin Capsule Tower, which was built in 1972 and is still standing in Ginza - nearest station is Shiodome. It looks very tired now ... in a way that reminds me of a student dorm...:
http://ja.wikipedia.org/wiki/%E4%B8%...83%93%E3%83%AB

If you really must stay in a capsule, then you can find capsule hotels near most major railway stations - such as this one near Shinjuku:
http://www.hgpshinjuku.jp/cap/cap.html#a2

But, since they charge you 4300yen to spend the night in a coffin surrounded by snoring drunks who missed their last train home, I fail to see the attraction of this "experience".