There is only one checkpoint at 15 miles (the turnaround point).  This is in the 18th century Fort Pezeries.  

You need to reach this point by 0330hrs otherwise you will be timed out (pace required 13:33m/mi).  Do not underestimate the pace required given the terrain and possible conditions.

Here there will be water, limited food and some shelter for a brief respite from the weather before setting out back to the finish.

Note that you will need to walk about 1km to our race support vehicle if you decide to retire at this point or are timed out.