using System.Collections.Generic;

public class Test
{
    public static void Main()
    {
        var item = new Foo();
        var inner = new List<Foo>();
        var outer = new List<List<Foo>>();

        inner.Add(item);
        outer.Add(inner);

        IEnumerable<IEnumerable<Foo>> data = outer;

        foreach (Foo foo in data)
        {
            foo.Bar();
        }
    }
}

public class Foo
{
    public void Bar()
    {
    }
}