I started with good intentions, really. I dedicated an entire day, from opening to closing, to Wales’ official history museum at St. Fagans, just outside the national capital of Cardiff. If it had been open longer (its hours are 10 a.m. to 5 p.m., daily), I’d have stayed longer; I did not want to shortchange what was by all accounts one of Europe’s most important museums. But surely seven hours would be enough to see everything.

It wasn’t. St. Fagans National History Museum contains more than 40 historic buildings from all over Wales on its 100 acres of parkland, behind the Elizabethan manor house known as St. Fagans Castle. “Over forty” is actually the official phrase and is intentionally vague, as new buildings are frequently being added; the official guide we purchased listed 57 separate places to visit. In fact, in the time between my visit and the British Heritage deadline, yet another building has been opened—a stone medieval church, spectacularly restored to the way it appeared in 1580. More on that later.

St. Fagans (pronounced FAH-guns) became part of Wales’ National Museum in 1946, donated by the Earl of Plymouth. At the time, it consisted of the fine old manor house with 18 acres of formal and informal gardens, backing onto a high, walled bank that carried a public lane, private and viewless, through the property; underpasses penetrated the lane bank to lead to 86 acres of woodland on the other side. For the next five years, the National Museum (whose main campus is in central Cardiff) was content for it to be yet another historic manor with gardens. Then, in 1951, a 400-year-old wood barn from Flintshire, far away in North Wales, became endangered, and the museum saved it by moving it to the northern end of the garden. The die was cast. The next year, the museum saved an 18th-century stone-built woolen mill in working order by moving it to the northern end of the garden’s large fish ponds, where the outflow could power the water wheel and drive the more than 200-year-old machinery. To this day, it produces Welsh shawls and blankets which can be purchased by visitors.

And, yes, I missed both of these. I had made the most basic of St. Fagans tenderfoot errors: I did not get the visitor guide in advance and plan my itinerary. You just can’t expect to walk up to St. Fagans and do it in one day. The museum has grown so huge with rescued buildings that seven hours is not nearly enough. As it happens, the wool mill and ancient barn (which is gigantic and built with curved oak trunks fitted together to form an A-frame) are among the farthest from the main building. Planning is essential.

About that main building: You can scour the visitor guide and the National Museum’s Web site without finding a single picture, or even a direct reference to it. They don’t even give its name. All you find are statements such as “the self-service café is in the main building.” There’s a reason for this. The main building is nondescript, low and modernist in design, built sometime in the 1960s. It looks like a middle school. Nonetheless it’s the real heart of the complex, where all the conservation and curatorial work takes place, along with Wales’ national historic library, four galleries of exhibits, a gift shop and the aforementioned cafeteria. Inside, it’s attractive and comfortable.

Penetrating the main building only takes a few seconds, as you don’t even have to pay admission; this place is free. The only reason to delay entering the grounds is that you are a fan of early tractors or historic costumes, in which case you are in trouble because the main building holds two large galleries on these subjects, filled with enough stuff to keep you inside all day. If you have not yet planned your day, stop now and buy the visitor guide. Pause for tea, and use this opportunity to circle your top 15 or so attractions. Plan a route and follow it. You’ll thank me later.

And what to see? The National Museum has intentionally shied away from any stereotypical view of “Welsh life.” You’ll find a Neolithic timber circle and an Iron Age village (both re-created from actual archeological sites), stone farmhouses, churches, stores, terrace houses, a huge 1916 Workmen’s Institute from Caerphilly, even aluminum-built prefabs from 1948. A working bakery produces and sells bread; a general store (with a fascinating back story) is stocked with early 20th-century items; a turnpike tollhouse is furnished as it would have been during the Rebecca Riots and a blacksmith works his forge.

For me at least, the most interesting exhibit was an entire terrace of row houses from the rough coal-mining city of Merthyr Tydfil a few dozen miles to the north. Now more than two centuries old, these six cottages have been furnished to show how coal miners lived throughout this period: 1805, 1855, 1925, 1955 and 1985 (when the museum moved the terrace). In front of each cottage stretches its garden complete with outbuildings, again carefully reconstructed for its period. It demonstrates how a half-dozen generations of working people adapted to exactly the same building structure as standards of living rose. If there is a museum that presents more visual interest and sheer enlightenment in a single exhibit, I have yet to visit it.

By all means, add to your schedule whatever building is being reassembled and restored at the time of your visit. At the time of my visit, crafters were working on 13th-century St. Teilo’s church, recently moved from Llandeilo Tal-y-bont. The church had been re-erected, and restoration experts were carefully re-creating its interior as it had appeared at the end of the Roman Catholic period. Painter Ffleur Kelly was testing period pigments before applying them to the wood panels of the loft; unlike the pallid interiors of the later Protestant period, this medieval church was awash in bright colors, its walls and woods covered in bright illustrations of biblical themes. In another room, Welsh woodcarver Ray Smith bent over his work with complete stillness, only his hands moving.

St. Fagans is one of seven campuses of the Wales National Museum, now emerging as the Smithsonian of Europe with its wide range of interests spread over numerous large and sophisticated buildings (as well as its free admission). The National Museum has five complexes in the Cardiff area; apart from St. Fagans and the original museum in Cardiff, the National Waterfront Museum celebrates Wales’ maritime heritage, and the Big Pit National Coal Museum allows you to go underground in an actual deep coal mine, while the extensive Roman remains at Caerleon, with their Arthurian links, make up the National Roman Legion Museum. Elsewhere in Wales, the National Wool Museum sits in the countryside east of Cardigan, and the National Slate Museum preserves an enormous open pit quarry in the shadow of Mount Snowdon.