Well, turns out that Eridor is not the only one that's hungry. As he ventured deeper into the lake, he forgot to take one fact into consideration: the deeper, the darker.
Being unable to see in the dark, Eridor fails to see a large fish heading his way. And by 'large' I mean 'capable of eating him whole in one bite'. Eaten instantly, Eridor couldn't even hope for a full tour, because he'd drown before he'd reach the 'exit'.

--- the bad ending ---