IGN goes hands-on with Tomb Raider: Underworld

Here. It's a playtest of the underwater section seen in recent screenshots, and some cavern bits later on with the big octopus, the Kraken. This sums it up:

While the code was still early, it was quite interesting to see how the developers have been crafting much of the game to play with cinematic camera angles and ambient sound effects to bring players into the action. In fact, the second half of the demo was intentionally stripped of the game's soundtrack, because the developers wanted to have only the sound of Lara, the Kraken and the environment to heighten the tension that was felt from each puzzle. While some visual details still need to be implemented (for example, the ping map was a basic 3D model that hadn't been fully realized), the game action looks like it will be non-stop when the title is released later this year.

Read it.