Skaugen
Google
First of all it's still free and a fun activity for families or friends to cool down!
Good potential, but a bit grumpy helpers. Awesome view to downtown but be aware that you can't leave the small area around the pier. Also they had a reservation website for the queue, which you should visit then you arrive there, but there is no functional wifi around (if you don't have mobile internet). Waiting times changes strongly, depends on how long the other guests are on the water.