Host a barbecue at someones home. Or go outside, to the park. Remember the sauce. And the beers. Combine it with quizzes and contests, or just enjoy the good company.
Have bubbles on the cool. Will make any celebration special.
Invite customers, stakeholders, other departments, or other companies with shared interest. Make it special. Ensure invitation, music, dancing, entertainment. Maybe team up with an event bureau to make it extra special.
Go archery shooting. Or shooting. Push your borders a little and feel the adrenaline.
Explore a foreign place. Or explore new sights in your hometown, and learn about their history and importance – you might get pleasantly surprised. Pretend to be a tourist and consider what you’d go visit. Alternatively go Geocaching.
Go to the theater, or go see a musical. Unwind.
Go retro. Find old console games, or join in online games. Join country competitions or just arrange it at the office after working hours.
In most major cities it is possible to arrange a laughter course. It will seem silly, but it is also a lot of fun, and can be a shared memory for the team to return to once in a while.
When a milestone is met, fill a jar of lasting candy, e.g. caramels, wrapped candy. That way, the celebration will last a little longer, and be a nice reminder of what you’ve achieved.
Do something extraordinary. Try out a hot air balloon, go hiking, wall-climbing, water-rafting, biking, segway, motorcross, sumo-wrestling. Challenge yourselves a bit, get some wind in the air, feel the tingle in the stomach, and have fun!
Send postcards from your trips. Share your greetings and travels with your team. Color up the office and hang them on the wall.
Make traditions around (some or all) holidays. Halloween, Easter, Christmas, national holidays. Decorate the office, dress up, create easter eggs in the code, make a quiz. Be silly. Have fun.
Acquire some fun toys, and play with them once in a while, to unwind and laugh together. An electric car, a toy robot, a quadroscope, whatever.