Oscarborg and narrow-water risk

Was Narvik the Norwegian example of German ships entering a defended narrow passage?

No. The likely example is Oslofjord and Oscarborg, where even light troops could make Drøbak Sound dangerous for a cruiser.

The likely example is Oslofjord rather than Narvik. German planners assumed Oscarborg Fortress was inactive, yet Drøbak Sound would still have been dangerous even if every heavy gun had been out of action. The cutting and embankment offered positions for riflemen, machine guns, and light mortars beside an exceptionally narrow passage. Ships would pass close enough for small-arms fire against exposed personnel, and a cruiser would have little room to escape prepared fire. Coastal defense here depended on terrain and forced proximity as much as the fortress's heavy artillery.