The main Iberia lounge at BCN is in Terminal B, towards the "M" gates and towards Terminal C. There might be another one dedicated to the MAD/BCN Shuttle (puente aereo). The main one is kind if hidden away, as you approach it looks/feels like you are going to exit back out of security in a corner; the door is to the left of the exits. Inside it is very roomy, with huge windows facing the inside of the departures terminal.

Both times I've been there, it has been virtually empty. Furniture is comfortable, there are tables/chairs and there are couches. There are 4 or 6 PCs with internet access, a smoking lounge, newspapers (mostly Spanish) and plenty of drink options including many types alcohol. Food options are more limited like packaged cookies, raisins, etc. General cleanliness only ok; bathrooms only ok. I didn't see any shower facilities but didn't ask either. Staff is cold as ice but will provide assistance if asked.