I don't see an existing thread on this. Stockholm Arlanda (ARN) has an affiliated Amex Lounge inside Terminal 5 which is the Star Alliance Terminal.
The lounge is located inside the shopping area which connects the F Concourse with the main, Gates 1-25, concourse. As you can see the signage is a little small.
Once inside go through this area past the couch and turn right and the lounge is inside. An agent checks your BP and Amex card
Seating is a little limited. Some couches, some tables and counters with power along a balcony overlooking the terminal
Snacks were pretty limited while I was there but there's also a menu
Overall a nice enough place though obviously lacking compared to any CL.