Across the sea bed.
This was to be a 2 week driving and camping holiday in the Netherlands. If you want to try this, you need to be aware that the Dutch love insane motorways that split and merge, with the ultimate being a doubly nested motorway. The Dutch drivers are also quite rude. Indicating to change lanes when motorways split means "please close the gap so I can't pull out", and standing at a pedestrian crossing means "please speed up so I won't be tempted to cross".
In the Netherlands, camping is not a hobby, it is an institution. The Dutch do not really go camping, so much as temporarily move house. They take everything with them, the kitchen sink for starters, followed by the widescreen TV, satellite dish, electric heater, and framed family photographs arranged neatly on their dedicated table (not kidding). This all requires space, so they take mega-tents, caravans, campervans and awnings. Hell, even their awnings have awnings - more on that later. We took a multi-room tent with us, more than 10 times the size of the last one I used for hiking, and it was still overshadowed by a small Dutch tent.
The campsites are immense, organised holiday destinations with neat plots and gardens, electric hookups, toilets, showers, washrooms, supermarkets, cyber-cafés, restaurants, playgrounds and swimming pools. Perhaps even a sauna. There are real campsites around - proper quiet campsites with real campers, but you may struggle to find one, and it will probably be full anyway.
The Netherlands is a tiny country, hardly bigger than Wales, but with a staggering population nearly 6 times the size. For nearly 3000 years, they have been struggling to find enough land for their people and have utilised the tidal flood plains of the German and Belgian rivers - vast salt marshes that they slowly cleanse and drain, holding back the sea and rising rivers with an extensive series of walls called dikes. There is virtually no uncultivated or unindustrialised land in the Netherlands, and their national parks are the size of a field, crammed between motorways.
Over half of the country lies below sea level at mean tide. For the last 800 years, wind power was used to pump water from below sea level, up a series of steps to the rivers above sea level, then through sluices into the sea. The draining causes the land to sink, further increasing the problem, which is then made worse by peat harvesting. These areas below the level of their surrounding river are called polders. Polders are covered in canals and ditches draining to the pumping reservoirs. The deepest point in the Netherlands is 6.76 m below sea level, at Zuidplaspolder, quite close to Kinderdijk.
Far from being a tourist gimmick, around 1000 windmills litter the country, pumping the water to the next polder. There are so many that like the castles in Wales, in the Netherlands, you can measure distances across the country in windmills, blurring past the windows and camera lenses. Current techniques use electric pumps, but these are still powered by endless forests of wind turbines.
Note: strictly speaking, the name of the country is Nederland (the Netherlands in English), but many people - including the Dutch themselves, and the tourism industry - call it Holland; a name that correctly belongs only to two of the provinces that make up the Netherlands. I will try to use the names correctly.
Note for any poorly-informed Dutch visitors: the English Empire ended over 60 years ago. What you may mistakenly call England is actually the United Kingdom (a.k.a. UK). Wales is not part of England and has been a separate country for nearly 60 years. England is a separate country in the UK. It does get very frustrating being constantly told otherwise, and having to defend the validity of this nation, just because you still use the wrong name. 60 years really should be enough time for you to catch up. I assume you would not appreciate me telling you that the Netherlands and Germany are "the same thing" (the phrase used in virtually every place where we had to register), just because Germany owned the Netherlands about 60 years ago, would you? Cheers ;)