Is a wekly typed List possible?

Question

For example I want to use a List of interface object.  But I want to insert into the list concrete objects that implement that interface.  But when I'm using the List I want to work with the interface types not the concrete types.  Is this
possible?
Example
interface ISettings{
List<ILocation> Locations {get; set;}
class ConcreteSetting1 : ISettings{
List<ILocation> Locations {get; set;}  <---- I want this to restrict this to accept only one particular concrete ILocation type
But in my usage I still want to work only with Interfaces.
ISettings mainSetting = ....
foreach(ILocation loc in mainSetting){
   loc.Process();
I already tried using generics like this
interface ISettings<T> where T : ILocation
and then the concrete class would be
class
ConcreteSetting1<T> : ISettings<T> where T : ConcreteLocation1
But I just found i had to specify the concrete type in the end which I don't want to do.  Just want to work with the interface types.
My Main problem and it could be a design flaw, is that all my ILocation objects share only one method, but the rest is unique to each.  So an object that using an ILocation can only use a particular one, not just any ILocation. 

Answer 1

I think you probably already realise you have a fundamental design flaw here.
If you need to limit these things to one specific type then that is mutually exclusive to only dealing with them by interface.
That's a problem.
You can do something like:
interface ISettings
List<MyLocation> Locations { get; set; }
interface ILocation
public class MyLocation : ILocation
public class MainSettings: ISettings
public List<MyLocation> Locations { get; set; }
and
MainSettings ms = new MainSettings();
ms.Locations = new List<MyLocation> { };
foreach(ILocation il in ms.Locations)
I'm just not so sure that gets you anywhere useful.
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