The trebuchet was the first working full-size reconstruction of its kind anywhere in the world. Its success prompted a two-month scoping project in the summer of 1991 called the Medieval Technology Centre: a series of workshops and a kitchen tent set up around the machine to see whether people would keep coming. They did. The centre was founded formally in 1992, and in 1994 a grant from Arbejdsmarkedets Feriefond paid for the leap from encampment to town - houses, tournament lists, a harbour, an entrance building. Ever since, the rule has been one major new project every year, which is why the site keeps growing sideways into new centuries of technology. It stands at Sundby on the Lolland side of the water, about four kilometres north-west of the centre of Nykøbing Falster.

The centre runs on the current calendar offset by exactly 610 years. In 2014 it was 1404, and so on. That offset is enforced with unusual seriousness. Staff and volunteers dress in period costume and, during opening hours, live as townspeople of a Danish market town would have lived - cooking, weaving, smithing, drilling with weapons. Glasses and piercings are not permitted. The inhabitants do not know what a mobile phone is, and will not pretend otherwise if you ask. The workforce is a mix: permanent staff, people sent by the municipality on job training, and a large body of volunteers coordinated by the Guldborgsund Guild. Even the restaurant plays it straight. The Golden Swann is furnished as the dining hall of a major Danish castle around 1400 and serves medieval food by candlelight; it is independently run but held to the same standard of authenticity as everything else on the site.

Reconstruction here is research, not theatre, and it produces the kind of rivalry that only experimental archaeologists have. Having built the world's first working trebuchet in 1989, Middelaldercentret went on to help build the one at Warwick Castle, which then held the record for the largest functioning trebuchet for six years. When the Danish machine's throwing arm broke, the centre replaced it in 2011 with one exactly five centimetres longer than Warwick's, and took the record back. Other work is quieter. Together with Moesgård Museum the centre reconstructed the world's oldest bronze-cast cannon. It has researched medieval textiles, winter habitation and the manufacture of war machinery, hosted a conference on black powder manufacture in 2010, and joined the third Galathea expedition in 2006-2007 to look into the materials of black powder production in India.

The harbour holds reconstructed vessels - the Gedesby ship, sailing as Agnete, along with the Bredfjed ship and the Egernsund pram - built with period tools like everything else. In 2010 work began on a medieval church, a reconstruction of Kippinge Church in north-western Falster. The technology park that opened in 2013 is the strangest corner of the site: full-size builds of medieval inventions that had never left the page, including a car drawn by the Italian engineer Giovanni Fontana and a perpetual motion machine that, faithfully reconstructed, does exactly what physics says it must. In 2014 a war wagon joined the daily display of siege engines, built from a depiction in the Hausbuch at Schloss Wolfegg and described as the first tank in history. Griffenholm, added in 2020, breaks the period entirely - treetop houses with steampunk interiors and a fictional professor hunting medieval monsters, aimed mostly at school groups and escape rooms.

Reenactment groups travel here from around the world, and since 2010 a week-long summer festival has widened the period on display; the Company of Saynt George, who portray the years 1460 to 1490, have been guests several times. The centre runs courses in historical weapon use for the historical European martial arts community, and film crews keep arriving - National Geographic on early diving equipment and throwing machines, the Danish film Vølvens Forbandelse, the German 12 Paces Without a Head, and in 2006 Mark Williams' Big Bangs, which used the site to blow up a boat. The numbers tell their own story. Around 110,000 people came in 1999, during Denmark's Medieval Year; in 2023 the figure was 37,768. Keeping a town alive in 1404 turns out to be harder than building it.