My fascination and knowledge of them comes from the beautiful book
Leven en werken van de kabouter (Gnomes in english) written by Wil Huygen and illustrated by Rien Poortvliet.I highly recommend it for the amazing illustrations and scientific observations of the life of gnomes, it’s really an enchanting book!
about them :They’re 15 cm tall without hats, have a 400 year lifespan if I remember correctly, are very strong, benevolent creatures, but do not disrespect them or..! They help out wildlife and farms if they live there. They’re pretty illusive so sighting is very rare.
(also here’s an amazon link, if you like, wanna have the book)