This cache is part of the "Get your kicks!" caching trail along Derby's radial bike route, Route 66!
As this bike path is very well maintained by Sustrans, I would strongly recommend completing the route by bike.
All caches are accessible on foot too though 
This cache is placed directly on the main cycle route (Shopping centre side of bridge). Please be aware that are likely to be lots of muggles using this route in the mornings and at school leaving times.
You are looking for a custom magnetic micro cache. The best place to park if doing this as a C&D is in the giant supermarket. You cant miss it!
The cache is clearly identified and hidden in plain sight. Until very recently there were some wires hanging out of the bridge; the fantastic people in the bridges team at the council have taken care of them very quickly to make the area safe.