Ah, nothing like the Kingdom of Zeal. Ever since I first played Chrono Trigger, I've wanted to visit that place. It's beautiful, it's advanced, it's magical. To top it all off, it's a floating island! One can either sit back and relax, or spend your time simply focused on whatever developments one is developing. It's a beautiful utopia...until the corruption.
Second choice is either Magus' Castle, or End of Time.