Both of mine are offline and involve something in an everyday space that others wouldn’t understand the significance of or possibly notice at all
First, the Hash House Harriers, the self-proclaimed “drinking club with a running problem”. It’s fun seeing chalk marks on pavement and knowing that a hash had recently passed by, even if it’s been some time since I’ve been.
Second, geocaching. Tons and tons of containers hidden around you that you might never see if not actively looking for it. It’s always a blast running into another person suspiciously looking about under a bench or whatever.