I dunno, the game is usually pretty good about providing hints to everything, even if the hints are pretty oblige at worst.
Kraka I just found because I wanted to chat with Snorri about something and just visited him at his work place. As for Alviss,
Click here to view the secret text
×Lots of people talk about how Svartalfar turn into stone when in contact with sunlight, and several people talk about a Svartalfar who was punished for courting an Aesir in Midgard. I made the connection with the strange rock pretty quickly, it was only a question of time until Aurvandel handed me the solution.
Similarly, for Skrymir's challenges,
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×Some of the Svartalfar talk specifically about his challenges, one of them mentions a race that is secretly a race against his mind. I found it a bit tenuous myself but you can get the idea that alcohol would slow his mind down. For the second challenge if you look at your opponent he is described as a fire elemental, so I mmediately figured that's what the ice flower is for.
There's been a couple puzzles that I couldn't figure out for the life of me and looked the solution up, but I can't remember which ones at the top of my head that immediately made sense after looking up. This game is pretty good about providing hints to you if you talk to everyone about everything and look at everything, especially compared to other adventure games that basically train you into using everything on everything else.