The wide-angle Nikkor (Nikon) 20mm f/3.5 is a super lens made only in the 1980s and can be bought used. Besides the excellent optics, the big benefit is that it’s small and light (only weighs about 8 ounces or 230 grams). Because of the smaller size, it doesn’t stand out when doing street photography and makes the camera easier to pack. It’s a manual lens which isn’t a problem. There’s no need for autofocus because the wide lens is in focus in almost all situations. The exposure can be estimated using the LCD viewfinder and I’ve not had a problem when using RAW files, which have a considerable exposure range. Nikon makes a f/2.8 version, but I find the extra f-stop is not worth triple the price and it’s a bit heavier and bigger.
I only recommend photo equipment that I own and have used for years. There’s always a new model or technology emerging, but I stick to gear that consistently enables me to take the photos I like when traveling. B&H is an excellent place to buy used and new photo and video equipment. Ebay is always a place to search for used models, but carefully check the seller’s reputation. I find the photo equipment reviews of Ken Rockwell to be helpful if I need to take a deep dive in technical specifications. A super resource on photo enhancement software and techniques is Robin Whalley. If you would like to discuss equipment options, contact me here.