I’ve stayed at the Sheraton and Gdynia CY. The CY is in the touristy area of Gdynia but there is little to keep you in that vicinity for more than a day or two. It has Gdynia’s priciest restaurant, but it is a nice space as is the Bar. There’s no lounge.

The absolutely central Sopot Sheraton does have a lounge open 06:00 to 23:00 with help yourself wine and beer during the entirety of opening hours, yep, you can start your day with a beer! It also has a very pleasant terrace overlooking the Pier Square for you to enjoy your breakfast, evening food, or just the cool beer. There’s 2 restaurants, a bar and a full Spa.

We didn’t stay at the Marriott but it doesn’t list a lounge so I assume it doesn't have one.