Bonfire

• A bonfire is a low-key birthday activity.Jupiterimages/Comstock/Getty Images
  
  Starting up a bonfire or lighting up a fire pit does more than set an appealing ambiance for an outdoor birthday party; it acts as a catalyst for several activities that young adults are sure to enjoy. By the glow of the fire, invite guests to pick up and play their guitars for a low-key jam session. Even favorite activities from childhood, like roasting marshmallows and making s'mores, are activities that are sure to please young adults, too.
  
  

Dancing

• Decorating the space makes dancing even more fun.Jupiterimages/Comstock/Getty Images
  
  Turn up the music, clear out some space for a dance floor and let the guests dance. Dancing is a popular activity for young adults at any type of party, including birthday gathering. Whether you hire a DJ or blast tunes from a computer, pick popular songs with a good beat that guests will enjoy dancing. To make the dance floor even more impressive, turn down the lights and rent a disco ball, flashing lights, strobes, fog machine and other decorative elements.
  
  

Games

• Friends will enjoy a game of poker.Jupiterimages/Polka Dot/Getty Images
  
  Playing a game is a fun activity that allows guests to get to know each other better, and enjoy themselves. Board games like Cranium, charades, or Catch-Phrase require a lot of participation, making them an energetic party activity. Traditional card games such as poker are classic activities for a young adult party and are especially well-suited for smaller birthday get-togethers.
  
  

Swimming

• Cool down and have fun.Jupiterimages/Brand X Pictures/Getty Images
  
  Taking a dip in the pool is sure to be a splashing good time for young adults at a birthday party. During the heat of the summer months, it's difficult to think of a more refreshing activity than plunging into a pool. Along with cooling off, birthday party guests can participate in a variety of activities. Set up a net and let guests play beach ball in the pool. Guests who want to revisit a childhood favorite can pick up a lively game of marco polo.