unmanaged c++ class in c#

Hey there guys, I have been using c# and c++ for sometime now and have found it to be alright  However, recently I needed to instantiate a c++ class, stored in an unmanaged dll in c#.  And since then, have got nowhere. 

Does anyone know how to instantiate an unmanaged c++ class, in c#?  And if possible without having to use c++ with managed extensions?

Yours - Ali