https://www.bungie.net/7/en/News/Article/cryo_archive_overview

Looks like a Destiny raid, but with PvP enabled. Sounds like the stakes will be extremely high since you can spend half an hour solving a puzzle only to get shotgunned in the back as you walk through the final door.

Also: It's weekend-only?

It is indeed, weekend only. Like Trials. Which is maybe a better link than Raids, AFAIKT.