I needed to learn about fifteen century Brittany for my WIP. Fortunately, I enjoy doing research. First, I hunted for books in our tiny local library, I usually find picture books with diagrams and simple, but accurate explanations in the children's section. I wasn't disappointed; I found books on motte and bailey castle construction, cross-sectional tutorials of moats and protective walls, descriptions of storerooms and housekeeping details.
Next I ordered books through a link to libraries throughout the state of Minnesota. I found an old book called "Medieval Living." Each chapter described a facet of medieval life, from meals to medicine, clothing to seiges, weddings to warfare.
I also hunted for used books at AbeBooks and Amazon. I found French travel guides,
books on the many Louis's of France, and theories about history of the Celtic races in France, England, and Wales. (The ancient Celts had only an oral history, so archaeologists have to draw suppositions from unearthed artifacts.)
I became the twenty-seventh member of the US Branch of the International Committee for the Defense of the Breton Language, an organization dedicated to raising awareness of the French government's campaign to eradicate the centuries-old culture of the Breton poeple through the suppression of their language. Breton is a Brythonic Celtic language related to Welsh, Gaulish, and Cornish. Cousin languages are Irish Gaelic, Scottish Gaelic and Manx.
A local book store owner sourced a Breton-English travel dictionary.
I researched Druids, menhirs, Duchess Anne of Brittany, castle ruins of Dinan, the Rance River estuary, traveling peddlers and the old story of Isolde and Tristan.
All of this, whirled together, became the historical setting for the timetravel part of my story.