3 months in Europe during summer 2025 and living rent-free. What would you do?

My partner and I have a unique opportunity to live in Ireland rent-free for 3 months next summer (July-September 2025). We're in our mid twenties (working full time) and would love to see as much of Europe as possible in that time. We are open to long weekends and a few week-long holidays. Would love to hear ideas you have on places to see, itineraries, getting around, etc. TIA!