Mix'n'match your own route from the Castle Grounds, Rea's Wood, and the Sixmile river path. Park at Antrim Castle Grounds.
Antrim town itself, perhaps surprisingly, has some fun if flat routes, with lots of singletrack and forest paths. If you are local, you will know most of these places
Suggested route:
Park in Antrim Castle Grounds, perhaps taking a spin round the Castle Grounds first (where there are a few neat ramps and drops), or at the Antrim Forum, and take the river cycle path to the Lough Shore.
Follow the car park round the lake, and head into Rea's Wood along the gravel path. At the clearing with the pile of stones on the right after about a mile, turn right for some twisting singletrack through the trees. Keep your pace up and this is great fun, but tiring!
Head back up to the main road along the gravel path past the old demolished DeerPark hotel, and across the Dublin Road onto Kirby's Lane. Follow the road until you come to Kirby's Lane car park, where you have a couple of options.
Turn left right down at the car park and follow the river path back into Antrim, or turn right and follow the path towards Antrim Technology Park.
After the big bridge, you can head up to the road to nip into the trees and tackle the ridge that runs high above the river all the way to the main airport road junction with the Belfast Road, or take a spin round the technology park.