How to access a TARDIS?

[rulandor]

The answer to this question might be trivial: Open the door and step in.

But as yet I have not watched a Doctor-Who-episode where the Real World Interface of a TARDIS was still functional. In the TTC, there are shown RWIs in the form of a Greek column or an organ instrument.

So, how to you enter or leave a TARDIS when the RWI takes the form of something which does not have, of itself, a door? Where do you "insert" the TARDIS key in such cases?

[Siskoid]

In the show, when this happens (the Master's greek column for example), people seem to pop out the back. I would imagine the keyhole appears as a response to the key, and the door materializes in similar response. I.e. it's there, it's just not visible on a seamless surface.

[Eryx]

I imagine that in that instance the telepathic connection comes into operation and you know exactly where the door is and how to open it even if nothing is visible.

[Escher]

Doors don't need to be in a fixed position do they? It could manifest when the surface was in proximity to the keyholder.

[Marnal]

In the show, the main door takes the form of a concealed hatch somewhere on the object. In some cases the crew has to get down on their hands and knees to enter.

According to the FASA rpg When there is no obvious keyhole to serve as a lock the keyhole merely needs to be pressed against a hidden sensor plate. The key will vibrate when it is held near the plate - making the lock easy to find.

[rulandor]

I imagined something like an invisible door, reacting to proximity of the key, but hoped for an explanation from people who know the relevant episodes.

Thanks!