Thanks Peter, I had thought that I might need to tempt a rat out of the portcullis to provide a more substantial snack than the spider which I'd been carrying around since the beginning, but just hadn't tried the most obvious way to attract a rat! Anyway, I eventually figured that out and have now finished the game.
Congratulations on a fantastic game, great setting, atmospheric and evocative descriptions and some really lovely, challenging but soluble puzzles make this a great game that I would very highly recommend to anyone looking for entertaining and challenging text adventures. The commands and gameplay were very intuitive which I greatly appreciate. I very much look forward to your future games!