Stairs of Cirith Ungol
The Stairs of Cirith Ungol were a pair of steep stairs cut into the Mountains of Shadow on the borders of Mordor. They led upward and away from Minas Morgul, the city that guarded the main pass through the mountains, to reach a higher and lesser pass guarded by the Tower of Cirith Ungol. The first of the stairs was the steepest, the Straight Stair, which led up to a narrow passage that seemed to go on for miles. After that came the second set of stairs, the Winding Stair, which led up to Cirith Ungol itself.
We're never told for sure who made the Stairs: they may have been originally carved by Sauron's servants, or perhaps later by the Gondorians at the same time as they raised the Tower to guard the pass. Whatever their origin, they were no secret to the Orcs that inhabited the Tower in the later Third Age, though Frodo and Sam were still able to use them to find a dangerous way into the Black Land.