It’s the hideout of Karliah, the supposed murderer and betrayer of the Thieves Guild. It’s loaded with traps set by Karliah for Mercer Frey. It’s also rigged with ‘bone chimes’ to wake the numerous Draugrs. Snow Veil Sanctum also houses a Draugr Overlord – a very strong undead who can also use certain shouts.
The Word Wall yielding the shout Disarm is within the structure.