Size : Up to 5 persons.
Duration : About 2 hours
Transportation : Walking.
Accessibility : Wheelchair accessible.
Tickets : Not necessary. Entrance is free.
Audiosystem : Not included (forbidden by the cathedral for small groups)
No luggages allowed inside. Appropriate behavior expected inside.
More information here : https://www.notredamedeparis.fr/en/visit/practical-information/safety-guidelines/