No, that door is in the Matterhorn. This door is in the upper story of Snow White's Scary Adventure. It is probably an access door to the pads on the roof of the west buildings.
Our revels now are ended. These our actors, As I foretold you, were all spirits and Are melted into air, into thin air: And, like the baseless fabric of this vision, The cloud-capp'd towers, the gorgeous palaces, The solemn temples, the great globe itself, Yea, all which it inherit, shall dissolve And, like this insubstantial pageant faded, Leave not a rack behind. We are such stuff As dreams are made on, and our little life Is rounded with a sleep. mycroft16 on Twitter
I believe the door you are referring to.. is simply a tech storage room nowadays. The room used to/probably still does, house the technical/sound board for the daily "sword in the stone" ceremonies Merlin once had. If you ever did see the show, you could easily spot the sound tech above.