How do I implement a method like myCountry.Towns.Add();

Question

I have a class called Country.  I can instantiate it by Country myCountry = new County();

It has method, AddTown(string townName) { ... }  which can be called like myCountry.AddTown("London");

How can I add an alternative method with identical functionality but which is called like myCountry.Towns.Add("London");

I cant figure out how to implement the '.Towns.' part of the naming structure.