Underground
Recorded per phase, because it differs per phase.
By day
Reachable on either route once the entrance is found — the walkthrough opens it as a vampire, but nothing about the door requires the night. Bring a torch; the narration recommends lighting one on the way in.
By night
The same entrance. Getting to the side courtyard that hides it is far easier as a vampire, which is the practical difference between the two routes rather than the crypt itself.
Relationships public material establishes, in the absence of map coordinates.
Seen in a developer-narrated pre-beta build, and deliberately cut short: Rebel Wolves halted the presentation inside the crypt to avoid spoiling what is down there.