If you start at Jim's Steaks at the corner of 4th and South (which is, frankly, not a bad place at all to start), you can walk south. As you filter past the body-modification shops and used record stores, you'll find yourself increasingly surrounded by a bunch of small, independently-owned fabric stores that specialize in high-quality, low-priced fabric. Some of them, like B. Wilke, focus on upholstry and decorating fabrics. Some stores specialize in bridal and special occasion fabrics. Further south are my two favorite all-purpose stores: Jack B. Fabrics and Maxie's Daughter.
You know how in some movies, a book-lover will enter an old book shop or library and find themselves in a sort of sanctum of tomes, where the ceilings are 15 feet high and the shelves reach all the way up, and the stacks are so close together that you have to walk through them sideways? This is what Jack B is to Fabrics. They carry all sorts, from heavyweight upholstery fabrics to draping sheers to poplins to embroidered silks. The fabric shelves are so tight together you will literally have to squeeze through them to get to the linens on the far wall, or point to one of the employees in the hopes that they know a trick to getting to it, and they stretch high above your head. The fabrics wind through the back of the store, and it's thanks to them that I made a little notebook for myself to keep in my purse that has the various patterns I have, the fabrics they use, and the amount of fabric for each pattern I need, because while you're browsing, it's easy to realize "oh! I could make a skirt out of that!" or "hey, this would make a great jacket!" The staff are a hoot, they go after one another mercilessly (highly entertaining) but are very helpful and know their way around. While I was there today I got some poplins for $5-6/yd, and then a faux-linen for about $8/yd. Update: On April 6 2013, a 3-alarm fire engulfed Jack B. Fabrics.
Maxie's Daughter is a block north of Jack B. This place is a little smaller, not quite as cramped, but has some very impressive stuff. They guy who runs it is a sweetheart and sold me everything for just $8/yd. This included a nice black stretch knit, some peachskins, some stretch denim (requested by mom), and a fabulous border-print stretch knit that I'm going to make a skirt out of. He had heavy houndstooth wool (which I would go for if I didn't have an allergy), and beautiful soft cashmere. While his selection isn't as broad as Jack B, he really pays attention to particulars and will offer breadth of options for a particular fabric. The staff will happily search the stacks with you looking for just the right fabric to match your current project. He specializes in vintage fabrics and draperies, but he's worth a quick browse if you have any sewing projects or "favorite patterns" that you would like to revisit with a different fabric.
There are a lot of great things about fabric row: The organized chaos, the inescapable feeling like you're treasure-hunting, the hysterical ball-busting that goes on between employees. But I think my favorite thing about fabric row is that the merchants don't squabble and poach from one another like you might expect. You would think that in a close environment like that, Store Y would try to prevent their customers from even going to Store Z by trash-talking Store Z's selection or quality. But this doesn't happen. The staff at B. Wilke will happily point you to Jack B. or Adler Fabrics if you're not finding what you need at their store, and vice versa. Each store is confident enough in its own selection and understands that the customer will buy what they like wherever they find it that they don't feel threatened by each other. As the woman who was helping me at Maxie's Daughter said as I mentioned I was going to check in at Jack B, "We're all family."
So here's the thing: Philadelphia is worth a visit on its own merit. It's got fantastic restaurants (where, unlike New York City, you can eat one of the best meals of your life without having to dip into your retirement savings), and some great museums, an arts district, and of course there's history out the yin-yang. So even if you can't just head out to Philadelphia for a day, the city has plenty to entice you to stay for a long weekend. But if you're out there and you're at all into sewing, you must take a few hours to enjoy fabric row.