I live in the New Forest and would agree with the description of 'undulating'. The biggest hill, as Graham Spratt says, is Marlpit Oaks at between 19 and 20 miles. I ride up it every day on my way home from work (having ridden down it on the way to work!) and it's a pig - long and deceiving - and usually straight into the prevailing sw wind! I'm running the half and will, thankfully, avoid it! Also, some of the miles in the marathon are on gravel tracks through the forest, which may or may not slow you down. Most of the hills in the New Forest would not be recognised as serious by those who live in Dorset, or further north in Yorkshire (Mike Shoemark) or the Lake District for instance, and I do wonder - when I come back from hilly places - why I find them hard. But they seem to drag on a bit. Most people I know who've run the New Forest marathon say that it's not a race for a PB. But the scenery is nice!!