We know not from where you start, so my suggestion:
Unknown field - Sleap - Warney Island - Ronaldsway - Newtownards - St Angelo - Knock - Abbeyshrule - Weston - Cardiff - Unknown field.
Make your overnight at St Angelo's and pop over the border to Blacklion for one of the best pints of the Black Stuff you are likely to find anywhere.
The Wombat