The best way to explore a city is by bike, and perhaps the best time for riding around a city is late at night.
While some places, like shopping centers etc have closed, it seems like a whole big part of the city opens up. When I first, came to Japan I remember thinking how different everything looks at night - to the point where I would often get lost among streets that would have looked familiar in daylight.
It would be very difficult to not come upon something new and interesting while out on a slow bike cruise through the old backstreets and alleyways of Yokohama.
Yokohama Rides and Rentals has 24 hour bike rentals available - lights included!