How fo you make friends as an adult?

Nearly said adult friends.😁 but seriously how do you meet you new people? I don't drink anymore I don't have any social groups anymore and the only thing I do in a public place is the gym, which lets face it ain't really the best place for meeting people.

I live in northern Ireland in a town of maybe 70,000 and the few things that I have an actual interest in just don't exist here.