An isthmus (rhymes with Christmas) is a narrow strip of land connecting two larger land areas, usually with bodies of water on either side.
The only reason I know this is because I went to college on an isthmus. You see, Madison is one of only two major US cities built on an isthmus, the other being Seattle. The Madison Isthmus forms the heart of downtown Madison and houses the twin engines of the city's economy, the University of Wisconsin-Madison and the Wisconsin State Capital. The Madison Isthmus is bounded by Lake Mendota on one side and Lake Monona on the other.
To be honest, while I was a student at the University of Wisconsin, I thought Isthmus was just the name of an alternative weekly newspaper that I read to kill time every once in a while. Only later did I realize the geographical significance of all those trips up and down State Street. Looking at this aerial view, it's amazing to think that I lived the better part of 5 years on that stretch of land known as the Madison Isthmus.
Every summer we spend about a week in Madison visiting with friends. My buddy has a great view of the isthmus from his house. We often sit on his deck at dusk, the Capital dome in the distance, the waters of Lake Mendota and Lake Monona shimmering in the fading light. It's a view I didn't even know existed when I was in college, but it's one I treasure now.