Hallerbos is a beech wood south of Brussels, in Flemish Brabant, Belgium, whose floor floods purple-blue for two or three weeks each April with millions of wild bluebells racing to flower before the leaves close the roof over them, and it is walked at dawn, when the mist between the trunks turns the low sun into shafts that land on the flowers and the roe deer are still out. The bluebells, Hyacinthoides non-scripta, flower in the light window before the beech canopy closes, from mid-April into early May depending on the spring, and the forest has a few days each year when green and blue overlap, the young beech leaves open but still thin, so the canopy glows acid-green while the floor is at full purple; the wood is gently hilly, and looking up a slope the flowers stack into one unbroken sheet with the smooth grey trunks rising straight out of it, while on the flat the same carpet shows its gaps. The bulbs press right up against the roots of trees far younger than they are, since the wood was cut by the German army in the First World War and replanted from the 1930s, and the bluebells are the old forest's survivors under new trees.
The ropes along the paths are not decoration: a footstep crushes the leaves and the bulb starves for the year, and the sticky sap inside those bulbs was once real glue, used to fix feathers to arrow shafts and later to bind books. The replanting was not all beech and oak, and a signposted route of about four kilometres leads away from the bluebell zone to a stand of giant sequoias planted in the 1930s, their spongy red bark and bulk absurd in a Belgian wood, the walk that still works in the eleven months when the floor is green. On the peak weekends the forest is closed to cars and shuttle buses run from Halle station. Hallerbos is a wood that turns blue for a fortnight, and the flowers do it before the trees can stop them.