The "Into the West Cycle Challenge" is taking place today.
As many as 200 riders departed Mullingar, Co. Westmeath this morning and are currently en-route to Galway City as part of a 300km round trip to raise funds for the National Breast Cancer Research Institute.
"It's something that is a very big challenge for a lot of people," said event Director Joe Duffy, speaking on Midland's Radio.
"It raises fantastic money for the National Breast Cancer Research Institute- in actual fact, we're just short of one million mark for the 19 years."
Riders are passing through various towns including Tyrrellspass, Athlone, Ballinasloe, Loughrea and Oranmore and will later be flanked by Garda motorbikes as they arrive into Eyre Square around 5pm.
They will stay overnight before returning to Mullingar tomorrow.