Walk! Deciding against the public transit was the best way to spend time in Paris. I got to take in details to and from the apartment that made my experience more lived in and less logistical. I understand the love affair with the city. One bite of a hot croissant from Boulangerie Utopie will unlock a great longing for the uneven streets of Paris long after your return flight.
It is a beautiful city. Although it was wet, grey and cold in late March (your March traveling companions should include an umbrella, hat, coat, scarf, and comfortable, rain-appropriate shoes). There exists a unique composition of contrasts from Rococo to geometry. A blend of cultures past and new emerge around each square - as if the ghosts of Christmas past and what's to come have left their day job to play permanent travel host.
If you feel you need to warm your heart and your hands with something familiar, you should try Le Café des Chats. People and paw watching is very universal. I also found any Café garmond, three tiny desserts and a coffee with milk, to be quite comforting and a petite way to taste your way through the city's flavors.