The Market
The Marketplace has everything you could possibly dream of, there's both an open stall market and individual shops in buildings, the buildings line a walkway that goes on for quite a ways. The market itself is, quite frankly, huge. The strip of booths and shops go on for miles. There are several areas to get food, open stalls that sell fresh produce, fish, and other meats, as well as indoor stores that almost resemble an old fashioned version of a Publix/Windixie. Food that's unique to your world can be found as well as things you've probably never heard of.
Moving on from the food areas there are stalls/shops that sell weapons, tools, clothing, medicine, and anything you could possibly think of. Each store/stall is manned by one of the native undead residents of the Underworld, these people go about their business in an almost mechanical way, though they can be stirred out of their foggy stupor if you try. There are also apothecary shops to be found if you search, though you won't find that the owners of the shops are very caring or helpful.
There are also bars and restaurants to be found in the market area, these are numerous and can be anything you can think of be it a fancy french restaurant or an old western dive bar, people from all over the world reside in this Underworld so it makes sense that the business are varied.
People are free to find stalls or shops that are empty, or stocked already without an owner, and start their own businesses. They're also free to start working for someone at their store/restaurant/whatever the undead will hire the new residents and you'll even get paid in coins!