Anywhere strangers tend to be around each other long enough to where small talk might be a welcome distraction: waiting in lines for something, sitting at a community table or bar/counter with mixed groups (especially while waiting for the rest of your respective friend groups to show up), sitting next to each other at a public event like live sports or a concert with downtime, volunteer events where you might be set up next to strangers doing the same thing, etc.
It's easier when there's a natural end to the interaction (your turn in line, the start of the sporting event), too.
Smartphones and headphones have made it harder, but there are still opportunities when people are bored and sitting around.