and head through the door
at the T junction, head straight
you end up in a burial room. On the far wall there is a movable stone block - it's a button - press it
Pressing that button has opened a secret door in the neighbouring area - but that door only stays open for a few sections, so you need to sprint back to the T junction, and thus time turn right
Which leads you into a large room, at the centre of which is a four-way crossing. Quickly head left here
and sprint through the secret door before it closes
and into the secret chamber behind it
To escape, you need to hit that switch on the wall, which opens the secret door again.