I am working remotely for 15 years, but from time to time I go to the local office; when I go to lunch, I just socialize with anyone that I see there and I either have an informal affinity (calling them friends may be too much) or I want to discuss a light business matter that does not require a formal meeting, but can be discussed over lunch.

Also I have a coworker in my team that is in the same city, but the opposite part, around 2 hour drive from me to his place. If we want to have lunch, we waste a lot of time (1 hour per direction for each of us); if we are in the office in the same day, there is zero cost.

I found small chat over lunch or a coffee break to be very effective in building relations with people you don't directly work with. This helped me many times in the past when I had to talk to someone and it was not a cold approach, so they made time to talk to me and help.