If you need help with the basic technique, check out this short video made in the classic game.

Another fun glitch is a window bug, which enables you to get inside the manor quickly, leaving the butler outside so he doesn't bother you as you explore. Start by using the corner bug to get on top of the assault course pillar nearest the bathroom window on the upper floor.
NOTE: If you haven't mastered the corner bug yet, you can still use this glitch by following the assault course in the usual way and then jumping to grab the windowsill.

Use the bug at this corner...

...and Lara will end up here.

Take a running jump to grab the windowsill...

...and pull up through the window...

...into the bathroom.
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