Of over 300 guard towers that had existed along the Berlin Wall, only one is still preserved. A short walk down a side street in the center of the city, it's physically close to the super modern shopping and buildings at Potsdamer Platz but separated by an entire era.
Now standing alone, it's really not an impressive structure; in fact, it was not obvious to find at first due to the surrounding trees. But the nonprofit organization that preserves it does a great job setting the context, showing pictures of the area, explaining how it was manned, and inviting anyone to go up for a small fee. It's great to see Berlin charge into the future with a new identity, but preserving and explaining the past is rightfully part of it as well.