Lowfolk Country is the "real" world of nonmagical mortals, referred to as "lowfolk" by the elves of Faerie. Elves of the Long Ago used to visit the lowfolk world either to play pranks on the lowfolk or for romantic assignations with the lowfolk themselves.
Elves of the late Imperial era seldom visit the lowfolk world except under duress. In part of the Ballad of Adler Young, it was necessary to travel through the lowfolk world to circumvent a Gap in Faerie. Adler also had to go there to receive Wiles training from Sheila na Gig. Later, Adler and Estmere had to travel to the lowfolk world to rescue Princess Edessa from the King of Spain.
There is an unpredictable temporal discrepancy between the lowfolk world and Faerie. Adler's party during the Gap incident spent only a single afternoon in the lowfolk world, but they arrived back in Faerie twenty years later.