This article is about the Class III road numbered C366 maintained by DfI Roads. For other roads numbered C366, see C366.
The C366 crosses the Lecale Peninsula in east Down. The road starts at a TOTSO on the B1 in Downpatrick and heads east. The road passes the western terminus of the C282 and meets the C283 at a crossroads as it crosses the peninsula. Eventually the road meets the A2 and continues into the coastal village of Ballyhornan. In Ballyhornan the C366 turns off to the south and ends where the road itself ends.