I read a sci-fi short story sometime before 1983 I think. In this story there were two characters who were deadly enemies. For some reason I can no longer remember they met on a large asteroid which was an artifact of some alien civilization. They knew it was an artifact because a gigantic concave mirror was embedded in its surface. The two characters approached the mirror from different directions and both became disoriented from seeing a perfect reflection of the sky at their feet. The two spacesuited men fell onto the mirror and began sliding around in slow arcs on the nearly frictionless surface. They spoke about their situation on their suit radios and figured out a way to attach a tether between them and use it to sling themselves off the mirror.
I've been wanting to reread this story for years, but I can no longer remember who wrote it. I'm pretty sure I read it in a book anthology rather than in a magazine. Can someone identify this story?