If weather is cooperating, why not to take the 175 bus and go to the Old Town? WAW Airport is very close to the downtown area. If you do not fancy public transportation (there are also trains available) you can take a cab or Uber (I think there were some fairly recent changes and only more expensive Uber Business cars have access to the airport). Otherwise your options are limited to the usual airport activities: shopping and lounges. You may visit both but F&B are the same. If you fancy plane spotting, the N/S lounge is on the apron level, so you will have a good view on apron/taxiways & one of the runways.