Click "play" to start the tour. Then either click the circles on the floor, or grab and drag the image, or use arrow keys to move and look around. (A mousewheel also acts like an up/down arrow key.)
Click "Change view" (lower left) to see a map.
There is a "Fullscreen" button in the lower right.
Interesting to know: each pale circle on the floor was a camera position. Try experimenting when looking around!