Bulwick's New Lodge Farm is a favourite. Lots of space inside and out.
There's a long route with a 71 km loop in Strava here, and a slightly shorter one at 63km here.
Here are some routes that we regularly use for club runs. Use the Categories to limit the routes you see. The compass points relate to where the ride goes from the clubhouse. Routes can be downloaded for your cycle computer, either directly as a GPX or via Strava for TCX.