In Stravanger the ship docks right in the town, so easy to wander in. The cathedral is in the centre and the old town is next to the port. (First two photos)
There is not a lot at Olden, but on one of our visits we took the trip on the little train that goes past the old church and round the town.
I haven't been to Helleslyt or Haugesund. The later is on the our itinery of our September cruise, but I do know that it is a coastal port.
A good source of information can be found at whatsinport.com