Netherlands as it would have been in the late bronze age/early iron age (the image is dated around 500 BC).

It’s clear that the West has now become one big peat area (laagveen).
The wetlands are now mostly in the North (where they still are, ‘de Wadden’) and the Northern provinces have become peat areas (hoogveen) as well (instead of oak forests).

(Compare to the stone age picture of the Netherlands.)

I found it funny to see that the Zuiderzee did nót exist at that time, we Dutchies can sometimes get sentimental about de Zuiderzee now being a lake (IJsselmeer), but it looks like that matches ‘old times’ even better ;) .