I have a 3.5 year gap on mine and used to dread this question. It came up during a second or third interview with a previous employer and the dread left as I answered honestly:

I was married to someone that was fortunate enough to have a lot of wealth and I didn't need to work. During this time we traveled a good bit and I went back to school for a stint to study music theory. I wouldn't trade those experiences for anything in the world but, alas, the marriage didn't work out and I had to go back to work. When reviewing my options I found a renewed sense of purpose in my career that transcends a simple means to pay my bills. I am very blessed to have had these opportunities and wish everyone was as fortunate.