That's Haiku Stairs. It was built by the Coast Guard as part of their Omega System (that sounds ominous, huh?) but it was a global navigation system before GPS was functional. The stairs allowed workers to service the antenna.
Last I heard, parts of the stairs are in disrepair and are usually slick with rain, as you can tell. You can climb the safer trail from the south side and get the same view. Don't try the stairs!