The quiet option is already in the official guide
SOAS says the designated quiet rooms during Welcome Week are S211, S214 and S216 in the Paul Webley Wing, and asks everyone using them not to hold conversations or play music. That is a very real campus resource, not an unofficial hiding place.
The same page points out that Russell Square is nearby if you want fresh air and a green space to recharge, which is useful when your brain needs something less fluorescent than another corridor.