When I got out of the Marines, I was single for a few years and traveled quite a bit for pleasure, always alone, and I always enjoyed myself. Chicago, Los Angeles, Grand Canyon, Minneapolis, Montreal, Quebec, NYC... The few times I traveled with a friend, I began to regret it rather quickly because I usually had to be more concerned with their schedule than I wanted to be. No need to worry about what others want to do when you are alone.
In a few of the cities I knew people and could hang out with them for a night or two but the majority of the time it was always a solo adventure. If I were still single these days, I'd still travel that way.