I expect your hotel is talking about the Gywnns Falls Trail. I just rode it for the first time this weekend, and I would say that it's not very suitable for 20+ mph riding.
As Derath said, hopefully some of the city riders will pipe up with some good mid-week route ideas. If that doesn't happen . . . I'd suggest that once you get here, pay a visit to Light Street Cycles -- it's walking distance from the Inner Harbor, and the folks there can definitely give you some routes.
As for weekends, if you head due north for about 20 minutes (up I-83 to, say, Monkton or Sparks), you'll find yourself in north central Baltimore County, my absolute favorite place to ride . . . beautiful scenery; twisty, low-traffic back roads; hills hills and more hills (many killer steep, but usually not too long.) The Baltimore Bicycling Club (http://www.baltobikeclub.org
) does a lot of rides in that area. Send me an e-mail, I'll send you my favorite cue sheet.
As for trails, there's a 10 mile loop that goes around BWI Airport, and connects to the Baltimore-Annapolis (B&A) Trail (13 miles.) It's paved and urban -- lots of places to stop and get something to eat or drink. http://www.bikewashington.org/routes/bwi/index.htm
. The North Central Railroad (NCR) Trail is a packed dirt trail, very rural and pretty, lots of trees, not many services, that runs from Ashland, MD (again, a short run up I-83) all the way to York, PA, about 40 miles one way. It's rideable on a road bike, but not terribly comfy if you've got very skinny tires. http://www.bikewashington.org/trails/ncr/ncr.htm