As I have written in the first part of this post about Svartalfheim, Nidavellir isn’t a location nor the name of the entire realm of the Duergar (Dwarves) and Dokkalfar (Dark Elves), nor is it a city. Nidavellir is in fact a labyrinthic complex of underground territores. There are thousands of corridors that lead somewhere, into houses, villages, halls, etc from Duergar that may or may not belong to a specific group.
It isn’t hard to find and visit Nidavellir, there is a huge trading area where one will certainly find members of each race of the Nine realms of the Norse cosmology, doing trading with the Duergar. However, one should not venture further than that, the trading area is easily memorized after a few times there in the company of a guide, but beyond it, as I have written, Nidavellir is a labyrinthic complex and it is easy to be lost there and even harder to find the way back.
Most come to Nidavellir to shop the many things that other races may also have and make them, but the Duergar make them even better. The underground territories of the Duergar is filled with the shops of all tpe of crafts and the Duergar are masters of whatever craft in existence.
They are a very skillful and talented race, and the thought of them making poor work, less skilled and cheaper, or trying to cheat someone, will be easily vanished as soon as one is able to see this race working and competing with each other to see who makes the best piece of a specific order. You may be certain that whatever you see being sold at their shops, is of high quality.