Steriti rink in the North End is my go-to. It’s an indoor rink but it’s free if you bring skates and not too crowded. Best part is you can go walk around the North End afterwards and Bova’s is right next to it.

Otherwise the rink at the Common is a classic but gets crowded.

I would look up random ponds near roads on google maps and drive out. Winter pond near woburn for example is a popular pond skating spot. Only go if the snow is already cleared/people are skating.