Sightseeing...

[Mjollnir]

Now, I've only done a grand total of one so far, so you'll have to forgive my lack of experience. But from what I've gathered from the ones I've read, there's context clues for the right time and weather from the riddles themselves.

For about 50% of them. The other 50% are random trial-and-error (or you go look it up). Not that I mind.