The battleship Mikasa. Embedded in the pier, it still looks impressive for a 114-year-old ship. You can see the crossroads of naval design, with aspects from the ships from the late 1800s, and some that would continue into the 20th century.
Here's one of the main examples of how ship designs changed. Newer battleships have walkways along the edge of the ship, with the superstructure taking up the rest of the space. Here the center is more like a sailing ship, with wide open deckspace between various above-deck rooms.
When not in battle, there were far better views from up here. The copper tubes connected the bridge to other important parts of the ship, like the engine room. Just shout and your voice would bounce its way down. This is still common on many more modern ships, since it's simple and works without power.
Because there are no more engines (and no more engine room), this room was set up with images and a video about the massive reciprocal steam engine. The Mikasa had about 15,000 horsepower, which could push it through the water at 18 knots.
The Mikasa is an important link from a historical standpoint between the iron-clad sailing and steam ships of the 1800s (of which there are a few still surviving) and the modern warships of the 1900s (of which there are many available to tour). Very cool to see.