The Rock, made by Sgt. Thundercok, is a map loosely based on the movie of the same name. There are two large bases facing each other with a lake in between them. Each base has the look and feel of a jail, complete with jail cells and guard towers. However, the objective of the map is not simply to capture the flag. What your team needs to do it break into the enemy base, and steal a key out of the warden's office. With this key your team needs to break into the enemy's gas chamber, and set it off. When this happens, your team scores, but that's not all! 10 seconds after the gas chamber is triggered, noxious gas is released through out the whole map. HEV suits become available, but only a limited number of them. Anyone who is not wearing an HEV suit or not underwater holding their breath will be killed.
There are a few neat features in Rock. Whenever an enemy enters your team's courtyard bright lights from the guard towers would shine on the door they enter from. Also, blasting through an underground mine with the demoman's detpack can open up a secondary entrance to each courtyard.
This version of The Rock is actually a mix between the original Rock, and its sequel Rock2. The water entrance to the enemy base incorporates the secondary path that leads to drain entrance in the jail shower from Rock2. However, the generator and the secondary door to the gas chamber from Rock2 are not present. In the TF1 version of Rock 2 your team could blow up the enemy generator and the courtyard lights and secondary door force field would cease to operate until the generator was fixed.
I think it's either a bug or simply hasn't yet been implemented, but the respawn-to-jail transporter isn't present in the version of TFC I played. In TF1 any enemy trying to enter a respawn room of the other team would be stripped of his weapons and thrown into one of the jail cells. They would not be able to get out until one of their teammates brought the enemy key to the cell to open it up, or when an enemy killed them.
The different water code for Half-Life is more apparent in this map. When you are underwater, there is a distance falloff effect (essentially volumetric fog) that hampers your sight at medium-to-far distances. In this version of Rock it is even harder to see underwater because the lake area is very, very dark. For example, you cannot see the underwater entrances from a few feet under the surface. You need to swim about half-way down the lake before you can see the lights of the entrances.
I always liked the Rock maps, as they were a breath of fresh air from your standard "2forts-esque" maps, and the TFC version of holds true to its name. The Rock never really felt like you were working a jail, but the atmosphere of the jail setting is definitely there. Unfortunately the library next to the wardens office was replaced with a bunch of file cabinets. (I think no one at Valve wanted to make the book textures!).
I have to admit that capturing the flag on Rock is the most satisfying of all the TF maps. There isn't any greater satisfaction than slamming the key down on the trigger and laughing at the other team as they scramble for HEV suits (gas masks) with the knowledge that there aren't enough suits for all of them! The best part are the enemies that chase you into the gas chamber. When you slam down the key they are all locked out of the room with the trigger (anyone in that room automatically receives an HEV suit), and all they can do is stare at you through the window as the gas is released.
The Rock is also one of the few maps that really require your team to use all the classes to be successful. Every class can play a significant role on your team, from the sniper picking off enemies as they jump into the water, to the spy that takes down the enemy sentry blocking the warden's office. The Rock is a great port of a classic map.