The 2016 race sold out in just six months .
The 2016 race attracted a record 22,000 runners , but interest in the 2017 race has been higher than ever - with organisers expecting 24,000 runners at the iconic Cardiff Castle start line on Sunday , October 1 .
The 2016 race sold out in just six months and attracted a record 22,000 runners , but interest in the 2017 race has been higher than ever - with organisers expecting 24,000 runners at the iconic Cardiff Castle start line on Sunday , October 1 .