The University of Wisconsin Lakeshore Path (also known as the UW Lakeshore Path) runs along Lake Mendota in Madison near the University. The most used part of the trail connects the tip of Picnic Point to the UW Memorial Union and the Union Terrace. The round trip is about 4 miles. Most of the trail is on a wide crushed gravel surface, but there are also segments of paved trail with soft shoulders that are separated for bike and pedestrian traffic.
The major marathon is the Mad-City marathon on Memorial Day Weekend. This race has had issues in the past, including being unprepared for the heat in 2010, forcing the cancellation of the race at the 4 hour mark.
Movin' Shoes keeps a Google Calendar of running events on their web site at http://www.movinshoesmadison.com/index.php?option=com_gcalendar&view=goo...
Fleet Feet Madison's event calendar also includes triathlon and duathlon events in addition to running - http://www.fleetfeetmadison.com/calendar
Many local races are listed in the Madison Area Running Series - http://www.madisonseries.com/Events/
The Lake Monona 20K Run is a great way to turn one of your favorite training runs into a supported run, or an excuse to go all out. The race is usually four weeks before the Madison Marathon, which isn't ideal for timing, but if you did an extra six or seven miles before the race, it would be a great long run.
