It's a fund-raiser for the suicide and self-harm crisis group Pieta House.
After a successful debut last year the Pieta 100 has expanded from three locations to nine this year.
One of those will set out from Birr tomorrow morning and take in Borrisokane, Nenagh, Toomevara, Moneygall and Roscrea before heading back to Birr.
There is a 50 kilometre route for the less energetic – the County Arms Hotel in Birr will hold a pre-registration evening between 7 and 9pm this evening.
