The Kale is an old fortress that saddles a hill in the middle of Skopje, overlooking the river, the old town, and the modern city. There was recently a fairly large archaeological dig on the site, which produce mounds of artifacts that are currently on display in the city museum. It is also undergoing a sort of restoration.
And it offers some lovely views. Entering the Kale through the old fortress gates:
A view of the tiled roofs of the old town. Those spires are mosques; the old town was predominately Turkish, although it has a large Albanian population now:
Still from the Kale, but overlooking the modern city: