Put signup sheets on outside of 3 room doors, each with (8) 15-minute slots. After guests arrive, have them add their names to the list on their choice of one door only. In 15-minute increments (timed), people go in and come out of doors in the order of their names, behind which are surprises. No one can tell what experience they had behind a door until the 2-hour time is over. We had a chair masseuse set up in one bedroom, a psychic doing readings in another, and a magician hidden in a third room. Meanwhile, others are playing a game in the living room and munching at a taco bar with lots of toppings. FUN party!
You could do less expensive alternatives, like a rock painting room, etc.
Celebrate Tasty Tuesdays
Fire up the grill or get out the chili pot! For over a year, Kev and I hosted "open table" Tuesday nights. We made a huge pot of chili or a bunch of tacos and if people wanted to bring a side dish, they did. We never knew who was coming -- we invited a core group to invite people who needed to get out -- the isolated or homebound or friends -- whoever. We wound up with 35-50 people a week from 6-8 on Tuesday nights and people brought guitars or whatever. We ate inside, outside, and throughout the house. Lots of fun.
Host a "surprise guest" dinner party!
My friend Lisa B. Nelson and I hosted monthly "Dinner with Jody & Lisa" parties. She is a multi-state Walmart lobbyist who managed Republican campaigns, so we came from very different social circles. Each of us invited 5 people who didn't know who else was coming. We booked a restaurant, date and time. Diners agreed to pay for their own meals/drinks and tip (we bought dessert). Invitees were to come with "Two truths and a Lie" to share with the other guests. Example: "I joined a group on a hilltop at midnight to hunt for UFOs; I was held overnight in a Mexican jail; I went shoe shopping with Robert Kennedy Jr." What is my lie? We learned so much about people and they had so much fun making new friends! Great memories.