Leiden Centrum is the medieval part of Leiden. It is roughly circular, with curving streets, rounded canals and densely packed housing. The city walls that once protected it from invasion, pillaging, etc. are no longer standing. The Witte Singel marks one border and the other contiguous canal has about 5 different names, which is apparently a Dutch custom. As an example, the street that I live on, Hooigracht, also has multiple names for different sections; Pelikaanstraat, Klokpoort, St. Jorissteeg, Orangeboom. This makes map reading that much more fun. Also, by inducing confusion, this custom protects against invasion, pillaging, etc.
Historic architectural planning aside, Leiden Centrum makes a great running loop!
Leiden Centrum Loop 5.62 km
and for comparison
Prospect Park Loop 5.40 km
Frankly, I'm shocked by how small Leiden Centrum is, especially considering the many times I've gotten lost inside of it. It's so small that I would have to circle Leiden three times to ride the same distance as one way of my old commute from Brooklyn to 86th street in Manhattan. Without that commute, my need for exercise is one big reason that I've started running again.
The Leiden Centrum loop is featured on the Leiden Road Runners club... and I look forward to running it! So far, I've been doing a shorter run at night to get used to running on cobblestones and bricks (also, I'm out of shape) and I have yet to see any other person running at 9 pm. I do feel like a freak. I've seen a guy peeing into the canal, drunk guys singing, kids smoking pot, but no runners. They must be on the loop!