Keswick Half Marathon Calendar When: May 3, 2015 all-day 2015-05-03T00:00:00+01:00 2015-05-04T00:00:00+01:00 Whether you are looking to complete your first half marathon or are a veteran of this even then this circuit of Derwentwater, with a loop into the Newlands Valley is probably the most scenic 13 miles 192.5 yards in the country.