You can make a fairly interesting and surprisingly hilly loop out of bridleways, byways and unsurfaced county roads in the area around but mainly west of Ancaster which is probably less than 30 mins from you. Inevitably it will involve some road work too though as theres a shortage of mutli user paths in Lincolnshire. Get an OS Explorer or Landranger map for the area, alternatively use the following link for limited free access to Ordnance Survey's maps online http://maps.the-hug.net/ .
I'm in North of Lincolnshire and only venture down there to ride a handful of times a year but for local to you it doesn't get much better. Thats not to say it's not worthwhile, good or enjoyable, it's just not technically interesting or difficult riding. I park and start from Ancaster railway station.