Though Krefeld is quite nice, it's more an industrial town than a big tourist attraction. So there's not so much to see except for what I wrote in the other columns.
But for its quite central location, you could stay there and explore the Ruhr Area, Köln/Cologne (40min. by train), Bonn (90min. by train), Düsseldorf (25min. by train), the lower rhine area (bicycle tours are said to be beautiful). You can also go to the Netherlands quite easy. Don't know about the trains, but the border's not very far, reachable even by bike on a day trip.