Today is a day of complete rest.
Assess how you feel. If you feel overly sore from the weekend's 13-miler, today would have been a great day to schedule a sports massage. It's probably too late for you to do so, unless you peeked ahead on the schedule, but consider this option for future Mondays as mileage builds. Let's talk about running form this week. But once runners attain a base level of fitness, how they run is worth some consideration.