The Virtual Tomb of Nakht has been changed from a version that required the Unity Web Player plug-in to a new version using WebGL. The new WebGL version has the advantage that it should work on any machine using a recent web browser, without requiring a plug-in. It does have some disadvantages though (at least in its current state). For one thing, the file size is HUGE (10 MB). If you find that the WebGL version does not work well for you, and that you preferred the previous Web Player version, you can find that version here: http://www.medievalist.net/unityworlds/oldnakht.htm
The new WebGL version employs a different system of navigation. You can look around just by moving the mouse. To walk around, you must use the W, A, S, and D keys. Note that S and D will move you side to side (strafing). To turn, you need to use the mouse. You may get a pop-up window asking whether you want to "Hide pointer." You should say yes. To get your cursor back, just hit the "Escape" key.
Enter the WebGL Virtual Tomb of Nakht