I'm trying to make a section where you pick up an item, and it takes you to a completely separate map than the one you were previously in. (You can't drop the item, so there's no need to go back.)

Is there a way to do this?

In the code where you decide whether you can or cannot drop it, there's also a portion that says "Do this after taking it". In that code, put "Move object to..." and tell it to move Player to WhateverNewRoom.

No, I'm fine in that regard, what I'm trying to do is make it take you to a separate area. So you go into a room, pick it up, and then it transports you to a different area that isn't connected to the area you were just in.

I have everything figured out apart from actually making the separate area.

You click the Make New Room button, no? You don't necessarily have to connect it to all the other rooms. You can even have unreachable rooms connected to nothing at all; I do that all the time to make a DebugRoom that holds stuff I don't want in the playable area.

You can have CoffeeRoom1 connected to CoffeeRoom2. You can have CastleRoom1 connected to Castleroom2. But you do not, at all, need to have an exit leading from the CoffeeRooms to the CastleRooms.

I had a feeling that the solution would either be super easy, and make me look like an idiot, or be ridiculously complex and confusing.

I'm not sure how to feel right now...

you have to clear/hide/disable the map/grid, move to new location/room, and then show/enable the map/grid again, possibly including populating/re-populating or de-populating it as well

all rooms have a built-in 'visited' Boolean Attribute, which the map/grid uses, so you can quickly 'foreach' through all of the desired rooms within a List Attribute, and set their 'visited' Boolean Attribute to true (populating) or false (de-populating), for the map/grid

http://docs.textadventures.co.uk/quest/functions/index_allfunctions.html (scroll to the 'g' section, and the 'grid_XXX' functions/scripts for the map/grid stuff)

the tutorial actually seems to cover everything for the map/grid stuff: http://docs.textadventures.co.uk/quest/showing_a_map.html