In my travels, it's the unplanned, unexpected, last minute things that often create the most special memories.>

here here - as i am want to pontificate it is often the things you see going between the famous museums/castles/churches, etc that stand out in your mind when visions of those are a blur - walking or taking public transport between the main sights - always more interesting in some ways than the actual sight - and this is what IMO bus tour groups - buses to the mobbed church or museum and then antiseptically bused to another mobbed church or museum, miss out on - what's in between the sights when going by foot, bus, tram, etc.