I'm looking for a fic that may have been Tony/Steve (possibly pre-slash), but I only remember a specific scene. The Avengers have been fighting evil and Steve and Tony are talking after the battle, part of which took place in or near a cave. Tony is paying attention to Steve but also very much paying attention to where the shadow of the cave entryway is so that he can be standing in the sun and not anywhere near the shadow or mouth of the cave.
ETA: Found! Link in comments