I remember reading a fantasy novel when I was younger. The book was in English, read in Canada in the late 80s early-to-mid 90s.
The big part of the book that sticks in my head is the party passing through a tunnel for a long time. Initially walking, then stooped over, then on their hands and knees, eventually crawling. At some point a party member ended up on their back, and they came upon a flooded section of the tunnel they needed to swim through.
The party was adventuring on some form of quest, I believe their goal was to pass information or to stop someone in particular. I'd put it in the fantasy genre. Swords, evil doers, magic and the like.