Active rest days can be a great way to counteract your desire to train but also keep you from vegging out on the couch. You can go for a jog, play some basketball, play disc golf (or regular golf), yoga, take a hike and explore nature in your hometown, or do some sort of mobility work or corrective exercise routines.
Being outside is great, but sometimes mother nature decides to be a dick and throw a wrench in your plans with rain.