Henneth Annûn, also called the Window of the Sunset, or Window on the West, was a hidden refuge of Gondorian rangers in the northern part of Ithilien along the Ephel Duath, the Mountains of Shadow. The waterfall cascading over the cliff-face had originally run through the cave itself, but was altered to flow over one of the entrances; this likeness to a window gave Henneth Annûn its name. There are two entrances into the cave system- one being the route through which Samwise Gamgee and Frodo were led, and the other being the window itself. At the bottom of the window was a bowl full of sharp stone knives.
Like all of the other hidden refuges of Gondor in Ithilien, Henneth Annûn was created by the Steward Ecthelion I circa TA 2900 in response to incursions of orcs from Mordor. Henneth Annûn was the longest-lasting of all the refuges in Ithilien. During the War of the Ring, Faramir, son of the Steward of Gondor, Denethor II, made it his base of operations. Caught in Ithilien, Frodo Baggins and Samwise Gamgee were taken there to be questioned by Faramir. Requiring the utmost security, the ring-bearer and his servant were blindfolded until arrival at the lair.
Gollum found the Forbidden Pool quite by accident whilst he was diving for fish. The penalty for coming to Henneth Annûn without permission was death. However, Frodo convinced Faramir to spare Gollum, and he was also taken to the cave blindfolded.
The refuge's garrison departed just after the Ring-bearer, and was used to hold the western half of Osgiliath against the forces of Minas Morgul.
- "This is the Window of the Sunset, Henneth Annûn, fairest of all the falls of Ithilien, land of many fountains."
- —Faramir, The Two Towers