I've reached level 29 (and this series appears to be difficult, because you can't bring your own items). Do these challenges ever end, or do they continue forever?

Yeah, I can get by using the beer from daily challenges and upgrading items from Valhalla levels, but if they never end I don't see the point any more.

It's really just a way to keep the game going for as long as you want to play it. Valhalla is by far the best way to upgrade your hats, which is why I got as far into it as I did. As the level of challenge keeps increasing, so do the level and quantity of hats you get for beating the challenges.

Did you get bored at 52 or did it become too difficult? If no one answers in a day or two, I'll mark this as solution. There are surprisingly few resources on the net for this game, considering it's pretty good.

I just sort of stopped playing and that was where I had left off.