I've heard that Tropea is very pretty, but after taking a look at the Google map of the area, I have no day-trips to suggest because I don't recognize the names of any of the surrounding towns. To make matters worse, Tropea has relatively little rail service. If you want to head north, you'll need to start with a 50- to 55-minute regionale trip to Lamezia Terme--an obvious place for you to research. But there are only two departures in that direction that are timed well for day-trips--one at 8:45 AM and one at 12:45 PM. You'll need to check schedules carefully to be sure you can get back to Tropea from the places you want to visit.
Perhaps there is useful bus service. That part of Italy isn't very well served by trains. A few years ago I wanted to travel from Sicily to Puglia, and I opted to take a bus. That's how slow and limited the train service was.