Eledryll - Abyssal Passage

You were tasked to enter a fortress and open the gates for the armies of a very generous duke waging war against his rivals in the region. The castle was rumored to be impregnable. However, by pulling a few strings and jumping through a few hoops, you learned of a secret passage, deep underground, leading to the bastion’s cellar. Of course, the route is not ideal and implies a walk of a few miles in a damp and dark cave, breathing who knows what kind of spores, alongside treacherous crevasses and, of course, dealing with the local wildlife. As dangerous as it might be, you may not have the luxury of a choice this time.