Restaurants/bars near Hotel Sax
I read the information at the top of the thread, suggesting you search by neighborhood - but I'm not sure exactly what part of town the Hotel Sax is in, other than knowing it's downtown.
I'm mainly looking for something interesting, maybe ethnic, for one person or a small group - and possibly somewhere nearby that serves decent food late on weekends.
The Loop is Chicago's historical and commercial central business district. Directly across the river to the north is the area which is named after its location: River North. The Hotel Sax is in River North, but it's within a block of the river, so it's walking distance from restaurants in the Loop as well. And just a few blocks east is the stretch of North Michigan Avenue known as the Magnificent Mile. So most restaurants in all of these areas are within a 5-10 minute walk of the Hotel Sax. (It's very conveniently located.)
Interesting and ethnic describes Frontera Grill and Topolobampo, the Rick Bayless restaurants serving creative provincial Mexican food. They are just a few blocks north of the Sax. Frontera Grill accepts only a handful of reservations and keeps most of the restaurant for walk-in traffic; waits for seating tend to be long on weekends, not so bad during the week. One person can sometimes be seated at the bar immediately. Topolobampo accepts reservations but is significantly more expensive. Both are good bets for lunch during the week, when the prices of the two are similar to each other, and Frontera Grill is open for brunch on Saturdays. Frontera is open till 10 on weekdays, 11 on weekends; Topo closes a half hour earlier. www.rickbayless.com/restaurants
Here are a couple more lively ethnic places nearby that are also good places to eat for a solo diner:
Sunda (pan-Asian) - two blocks north of the Sax - dinner till 11 weekdays, midnight weekends, lounge open an hour later than that - www.sundachicago.com
Nacional 27 (Latin fusion) - 3/4 mile northwest of the Sax - dining room open till 9:30 weekdays, 10:30 weekends, tapas ceviche and dessert till midnight weekends - www.nacional27.net
There are several places that serve ethnic food in a "small plates" format that will also suit your needs (and eating at the bar works well for a solo):
Quartino (Italian) - a few blocks north of the Sax - kitchen open till 1 a.m. most nights - www.quartinochicago.com
Cafe Iberico (tapas) - a few blocks northwest of Quartino - open till 11:30 weekdays, 1:30 weekends - www.cafeiberico.com
Avec (Mediterranean) - a mile west of the Sax - communal seating works well for the solo diner - kitchen open till midnight during the week, 1 a.m. on weekends - www.avecrestaurant.com
There are many, many more restaurants within a short walk of the Hotel Sax, but these are the ones that come immediately to mind based on what you've specified. If there are other (i.e. non-ethnic) types of food you might be interested in, such as steaks, seafood, contemporary American, deep-dish pizza, etc, just ask!