Euling C.
Yelp
I visited Allas Sea Pool while on vacation in Finland, and it was fantastic! I would definitely recommend the experience.
Entry to the pool is €12, which I found to be very reasonable. The price gets you an electronic wristband, allowing you entry into all areas (pools and saunas) as well as locker access for a 10 hour period. Re-entry is also allowed, which was extremely useful for me - I was staying a little bit outside of the city, and so I brought a day pack, stashed it in a locker and went to explore the city before returning later in the afternoon to swim.
There are three pools which overlook the marina area, so it feels like you're swimming right by the ocean. They are different temperatures, and I believe one is a seawater pool. The pool deck is large and there are a number of deck chairs available for use, however it's also possible to just relax on a towel.
Allas additionally has three saunas - male, female and mixed. They are not huge and can fit maybe 15-20 people each, so bear in mind at busy times it could get crowded. A swimming costume is required for the mixed sauna, however in the single sex saunas it is traditional to go in the nude. I believe all saunas are set at the same temperature, therefore there isn't much difference between any of them besides the people.
There is also a restaurant and bar onsite, and on the day that I was there, a music festival was running as well, however this was an additional cost not previously included in the entry price.
Overall, I'd say Allas is a great place to visit, whether or not you want to swim. Entry is cheap enough that you could go over for a quick dip and also experience Finland's sauna culture, and still get your money's worth. The staff that I encountered were very friendly, and I would definitely return if I ever find myself in Helsinki again!