Lava can be sharp and unstable. Do not run off-trail.
The trail starts off as a paved path. When the trail splits turn right to continue down a flight of stairs to a cinder trail. There are a few pumice rocks in the trail you could trip over if you're not paying attention but it is fairly smooth and easy, making this a great run through various lava flow features including a splatter cone and adjacent mound. The whole park is entirely surrounded by pumice and the evidence of a former lava flow which is pretty cool. It is a good way to stretch your legs in the middle of a long drive.
The longer drive through Wupaki National Monument was a great way to soak in the sights and lava landscape.