The capital of Croatia provides multiple options for a runner to perform all kinds of training...
Options covered here are for flat-course running. If you need trail-running experience, try Medvednica mountain, which is reachable on public transport.
1. Sava river
A flat path goes along the river for many miles.
This bridge is known as "Hendrix bridge" among locals, since someone draw "Hendrix" on it as a graffiti.
There some benches, but no places to throw garbage. The path to the left of the benches can also be used for running and it's softer than the main road.
Running is popular in Zagreb. Even mothers run with their toddlers.
Statues run, too.
Not this one.
2. Mladost (Youth) stadium
Good for speed-work. Fairly soft and flat surface.
Access to the stadium is absolutely free (except some team training days).
3. Bundek lake
The lake is surrounded by branchy pathways (asphalt).
There are lighting poles, benches and litter-bins.
The park surrounding the lake is very popular recreational place in summer.
Bunddek's disadvantage is its locaton on the Southern side of Sava river, which means crossing a bridge is you stay in the central part of Zagreb.