We do Paris and London a couple of times a year over 3 or 4 day weekends, and IMHO Paris is easier of the two just because we don't do theatre every day. We walk around our favorite areas of the city, see a museum or two, walk in a garden, windowshop (till the Exchange rate improves I'm not even tempted to buy) and have some wonderful meals. We take an evening flight over and always make reservations for a fabulous lunch on our last day before leaving to catch an afternoon return.