User blog comment:Alchimous/Teleportation Matrices/@comment-4536066-20121004185732

Not that my evaluation is any more or less accurate, but it was actually my interpretation that you could teleport anywhere not-teleblocked if you had the know how and runes available to you, just that the spellbook coordinates have been smoothed out and tested and refined to involve an elegant, clean-cut number of runes that take the user to a specified location reliably. As with all spells, an educated mage could slightly alter a spell to slightly change the destination under the same principle that an educated mage could alter the destination of a teletablet (see: Love Story). For example, he might be altering the Varrock teleport slightly to take him to the castle courtyard instead of the town square. The downside is that using an altered spell that hasn't been rigorously tested and refined is more dangerous and you're more likely to, like, end up inside a wall. This doesn't change anything about the question, really, but I just thought I would share my take.

On to the actual question:

I would agree that area teleblocks work both ways. The same magical disturbance that prevents/scrambles/whatever teleportation energies and render them void upon an exit attempt would scramble them from the other side, too. Just looking at it analogically, say you have a doorway (the abyssal portal) and you shut the door and lock it (teleblock the area). While the door is locked, you can't get through from either side of the doorway. On one side - the side with the lock on it (where the teleblock was cast from) - you can get around the issue by unlocking the door (by disspelling the teleblock) and proceeding as normal, but on the other side you're just plain locked out until the door gets unlocked.

Now, this brings up all kinds of other subtopics that align with the second half of your question; are there other doors that lead into the same room that you can use to enter, therefore getting around the locked door?; are there walls around the doorway, or is it just a frame with a locked door that you can walk around?; do these doors have keys that allow people to unlock them from the outside (and therefore teleport in), or is the only way to unlock the door from the inside?.

As for using "other doorways," I'm not sure. I think the root question behind this would be, "Can different kinds of teleport styles (e.g. Lunar vs. Ancient) both be blocked by the same teleblock?" I don't know. Have you made any observations that speak to it? I suppose the closest hint I have suggests no, because you can't use teleports from any spellbook leave a teleblocked area, so it's likely that you can't use them to get in, either.

As for a free-standing door frame, I think that would depend on the specific instance of the spell and the details of how it was cast. Take Ardougne castle, for example; if you set up a teleblock on the building that protected everything within its walls from teleportation, a person might still be able to teleport onto the roof and then descend in unnoticed by all but the archers guarding the roof. A mage with foresight might anticipate this and create the teleblock spell such that it would float as a bubble around the castle, but then a teleporter might be able to teleport (with precautions in place, like a glider or air magic) into the air above the bubble and again descend down onto the roof. It causes complications for the intruder, but could still be gotten around. However, if you have a perfectly walled-off area, like Marvolo's base, which is underground so someone teleporting nearby would end up teleporting into solid ground, so that sort of loop hole obviously doesn't work out so well.

Keys. I say that keys can be arranged, although they would probably be difficult to create, and may be very dependant upon physical triggers. The most glaring example of this is the wilderness lever that connects the deep wilderness to a workshop in Ardougne, allowing teleporting between the two places despite the area teleblock in the wilderness. (Although, on a separate note, I think being directly teleblocked in the wilderness stops you from being able to use the lever, so I'm not sure where to go with that. Maybe a teleblock cast directly onto your body is more potent and intense than an area block? Or maybe the key is only effective for one given spell.)

Ah... I think that was what you were asking.