Info on travelling in the Netherlands

Having just returned from another fantastic holiday in France, we are feeling very sorry for ourselves that it's back to work today and have already started thinking about the next trip! 

We fancy a change from France and were looking at sites in the Netherlands. Does anyone have any experience of travelling here? What's it like? What are the travel times from Calais? Any experience of sites? We usually take 2 weeks and travel to 2 or 3 sites. 

Any info would be much appreciated and will be a great antidote to the first day back in the office