It is a hidden room that is only accessible during a specific time of day, and you need to have a special item to enter.
Here are the details on how to find and access Cliffhanger:
* Time: The entrance to Cliffhanger only opens from 9:00 PM to 9:00 AM Neopia Time.
* Location: It is located behind the "You Are Here" sign in the Lost Desert. You need to click on the sand behind the sign to reveal the hidden entrance.
* Item: You need a Desert Treasure Map to enter. You can obtain one by completing certain quests in the Lost Desert, like the Ancient Tomb or the Pyramid of the Sun.
Once you have the map and are in the right time frame, click on the hidden entrance behind the "You Are Here" sign. You will be teleported to Cliffhanger.
Note: Cliffhanger is not a constant feature on Neopets. Sometimes, it's removed from the game for special events or other reasons. So, it might not always be accessible.