I first heard about this when travelling in America and talking to a group of people who mentioned a travelling community online who track where they go and how far they are from visiting all UN countries. Then beyond that any other territories. You have visited the UK but have you been to Gibraltar, Bermuda, Pitcairn, South Sandwich. There's so much more to the world to explore.
More than just ticking off countries and regions of the world (I'm very list based so that gets the dopamine going), it's about meeting like-minded people and getting advice from them too. Being able to ask what a particular border crossing in two remote countries in Africa is like, and having someone who was there 4 months ago reply is incredible.
I was fortunate to go on a trip to Syria and Lebanon last year, with one to Nepal and India scheduled for this year - all because I took a step into the unknown and found a place that matched my goals so perfectly.
If you enjoy travelling for any reason, this is a great place to start.