For my birthday this year, i invited friends to a party on Saturday but didn't tell them the location. I gave a list of questions they could ask me. Whoever finds me in the fewest questions wins a prize. 

Each friend showed up that day excited to tell me about their detective work & misadventures in tracking me down. Everyone had a lot of fun! 

I definitely recommend this as a party idea or meetup activity. It was much easier to organize than i expected.

Advice:

• Use this question list:
  • I'm at <GPS LOCATION>. Are you within <DISTANCE> of me?
  • Send me a photo of you.
  • Send me a photo of a tree.
  • Send me a photo of a street.
  • Send me a photo with your camera pointed straight up.
• You could also add these questions:
  • Send me a photo of a restaurant.
  • Send me a photo of the tallest thing around.
  • Send me a photo of the oddest thing around.
  • Send me a photo of your favorite thing around.
• Tell guests when exactly the game starts. I told guests we would play 3 rounds, at 1000, 1300, & 1600 respectively.
• Set reminders for yourself so that you have enough time to travel to the next round's location. You will be distracted.
• Don't let guest expectations get too high about the party aspect. If you plan to be simply sitting on a park bench, tell them to expect a chill hangout after the search. The search is the main focus. Also note that your attention will be divided between guests that have arrived quickly and your phone, as you answer questions from slower-arriving guests.
• Tell guests what to wear. I said: Dress for walking around outdoors and/or casual indoor places.
• Tell guests whether they can bring their children and/or dogs to the secret location.
• Ideally, your secret location should:
  • Have a restroom
  • Be somewhere guests can step into without paying money or feeling awkward
• My secret locations, for example, were:
  • A coffeeshop next to a bookstore
  • Outdoor seating at a restaurant (that suited multiple diets)
  • A park with a good view
• Encourage guests to take public transit, rideshare, or carpool, because solo drivers will find themselves spending a lot of time looking for places to park between every question, which is rather tedious. (Or they will text while driving, which is dangerous.)
• It is okay to crop your photos if details in the corners would end the search too quickly. A determined guest is very good at finding information in a photo!
• Conversely, if a guest isn't having fun, encourage them to ask lots of questions, or give hints.

(I came up with these rules by drastically simplifying the show Jet Lag.)

I recommend this!