I used to arrange this sort of informal house party for our development team. We'd rent a big house and bought food and drink, and then we'd split the check, and some people would come early or stay late and talk shop.

And we'd have a bonfire and roast marshmellows and bratwurst. Was fun.

We did it out in the country, on a good train/autobahn route, and just made sure that there was an actual inn, nearby, so that everyone could rent a room.