To the North, the cell at the end is empty. Around the corner, the 10' wide passage heads 50' South, then opens into a 20' wide East/West corridor. The corridor extends 20' West from the 10' passage, and 50' and then turns South (so 70' o the wall on the Eastern side, 100' overall East/West). On the North wall, 40' East of the passage you are enter from is another 10' passage heading North. The bend to the South continues to be 20' wide. On the South wall, 10' from the West end is a door (so not quite opposite the passage you enter from). Just past the corner to the East is a 10' passage (so basically, there is 20' of North/South wall at the corner, then a 10' passage).
Door, passage North, passage East, or passage South?
Amadeus draws himself up to his full height (which admittedly isn't all that much) tries to look all arcane and mage-like (and largely fails to do so) and unleashes his Sleep spell on the loathsome arachnids.
(O.O.C: Assuming his own colleagues aren't going to get caught in the crossfire, of course. If that's likely to happen he'll concentrate on providing light and keeping clear of trouble. )