I always figured it was just on the other side of the kitchen. That's the only other door that it would be. And there's an episode where Michael is in the kitchen, and Toby comes from that other door to ask Michael something. So if I am correct in inferring that Toby was coming from his office, and his office is in the annex, then the annex is on the other side of the kitchen. Maybe, maybe not.

that sounds right, but i remember once that i saw toby by accounting i think.

Yeah, it's past the kitchen, next to the break room.

If you watch "Drug Testing," you can see how the kitchen leads to the annex, which then has a door to the break room.