Collectible Card Game Headquarters

Where is this? I've beaten every Commander game on the board (and can visit any square) and Urza, but I don't see where it is.

Sorry for the late response - it's a secret area on Dominaria, rather difficult to spot (probably can only be spotted randomly), not sure if anyone has seen it already or not...

Here's a gentle hint: you need to carefully examine the planes once you defeat the supposed "boss" of the plane (as to who the boss is, you can understand that from the plane description).

If that doesn't help, here's a more direct explanation under the spoiler tag

| Open

Basically, you need to open your Planeswalk screen right after you defeat Demonlord Belzenlok, and then you'll find Time Vault among the options. However, if you step away from that location, the portal closes and you will not see it anymore (until you beat Belzenlok again, that is).

- Agetian