[SessionState(System.Web.SessionState.SessionStateBehavior.Required)]
public class HomeController : Controller
{
    // GET: Home
    public ActionResult Index()
    {
        return View();
    }

    public async Task<ActionResult> Check1()
    {
        Session["Test"] = "Check";
        System.Diagnostics.Debug.WriteLine("Session: " + Session["Test"]);
        await Task.Delay(20000);
        return View();
    }

    public ActionResult Check2()
    {
        var test = Session["Test"];
        ViewBag.Test = test;
        return View();
    }
}

@{
    ViewBag.Title = "Check1";
}

<h2>View with Delay</h2>

@{
    ViewBag.Title = "Check2";
    var check = ViewBag.Test;
}

<h2>Immediate View @check</h2>