I want to add a tip that took me a while to really learn how to manage. Traveling takes time. A 4 hour train trip, plus finding your way to the start station and from the end station, can easily become 6 hours. Add to that packing up, then getting a map and getting oriented, and settling in at your new destination, plus finding a meal to keep yourself alive, and you have 7 or 8 hours. Most of my 5 day trips became 4 or 4.5 days of actual city time, so that can be a disadvantage of a weekend hop down to Greece or trying to plan a really efficient trip in a particular city.