The distinction between .MapRoute for MVC controllers and .MapHttpRoute for Web API controllers is crucial to understand.

I added the content in white to RouteConfig.cs:

using System.Web.Mvc;
using System.Web.Routing;
using System.Web.Http;
namespace SomethingSimple
{
   public class RouteConfig
   {
      public static void RegisterRoutes(RouteCollection routes)
      {
         routes.IgnoreRoute("{resource}.axd/{*pathInfo}");
         routes.MapRoute(
            name: "Foo",
            url: "Foo/{id}",
            defaults: new { controller = "Foo", action = "Index", id = UrlParameter.Optional }
         );
         routes.MapHttpRoute(
            name: "Bar",
            routeTemplate: "Bar/{id}",
            defaults: new { controller = "Bar", id = UrlParameter.Optional }
         );
         routes.MapRoute(
            name: "Default",
            url: "{controller}/{action}/{id}",
            defaults: new { controller = "Home", action = "Index",
                  id = UrlParameter.Optional }
         );
      }
   }
}