How well do you know someone? How well do you know your friends? Do you even want to know them even more? Install this app, find a common period and swap houses for a while. It should be a creativity booster and eye-opener as location and surroundings pretty much define your mood. Included is at least one meeting with non-mutual friends.
I don’t know whether a checklist at the end of the period with tips and tricks to improve quality of life and a quiz to see if you got to know your friends even more is needed. It’s all in the experience, i presume.