In the writing challenge, the translation from english was that person dreamed of going to Paris, I translated this as y rêver thinking rêver à aller

Bonjour Ann !

This one is quite a tricky case!

The fact is that rêver à + [quelque chose] is very rarely used, and always in a figurative context, something you're considering: 

For every other case, it would be rêver de.

And to say to dream of [doing something], you'll always use rêver de [infinitif]: 

I hope that's helpful!
À bientôt !