Илья

public class SeoController : Controller
    {
        private const string SitemapsNamespace = "http://www.sitemaps.org/schemas/sitemap/0.9";

        [NonAction]
        private IEnumerable<SitemapNode> GetSitemapNodes()
        {
            // вот так добавляются статические ноды
            var nodes = new List<SitemapNode>
            {
                new SitemapNode(ControllerContext.RequestContext,
                    new {area = "", controller = "Home", action = "Index"})
                {
                    Frequency = SitemapFrequency.Monthly,
                    Priority = 0.5
                },
                new SitemapNode(ControllerContext.RequestContext,
                    new {area = "", controller = "Home", action = "About"})
                {
                    Frequency = SitemapFrequency.Monthly,
                    Priority = 0.5
                }
            };
              // а вот так динамические
                var items = model.Collection.ToList();
                foreach (var item in items)
                {
                    nodes.Add(new SitemapNode(ControllerContext.RequestContext,
                        new {area = "", controller = "Home", action = "blablabla", link = item.Id})
                    {
                        Frequency = SitemapFrequency.Weekly,
                        Priority = 0.8
                    });
                }
        }

        [NonAction]
        private string GetSitemapXml()
        {
            XNamespace xmlns = SitemapsNamespace;

            var nodes = GetSitemapNodes();

            var root = new XElement(xmlns + "urlset");


            foreach (var node in nodes)
            {
                root.Add(
                    new XElement(xmlns + "url",
                        new XElement(xmlns + "loc", Uri.EscapeUriString(node.Url)),
                        node.Priority == null
                            ? null
                            : new XElement(xmlns + "priority",
                                node.Priority.Value.ToString("F1", CultureInfo.InvariantCulture)),
                        node.LastModified == null
                            ? null
                            : new XElement(xmlns + "lastmod",
                                node.LastModified.Value.ToLocalTime().ToString("yyyy-MM-ddTHH:mm:sszzz")),
                        node.Frequency == null
                            ? null
                            : new XElement(xmlns + "changefreq", node.Frequency.Value.ToString().ToLowerInvariant())
                        ));
            }

            using (var ms = new MemoryStream())
            {
                using (var writer = new StreamWriter(ms, Encoding.UTF8))
                {
                    root.Save(writer);
                }

                return Encoding.UTF8.GetString(ms.ToArray());
            }
        }

        [OutputCache(Duration = 60*60, Location = System.Web.UI.OutputCacheLocation.Any)]
        public ActionResult SitemapXml()
        {
            var content = GetSitemapXml();
            return Content(content, "application/xml", Encoding.UTF8);
        }

        [OutputCache(Duration = 60*60, Location = System.Web.UI.OutputCacheLocation.Any)]
        public FileContentResult RobotsText()
        {
            var content = new StringBuilder("User-agent: *" + Environment.NewLine);
            content.Append("Host: ").Append("www.твой-домен.ru" + Environment.NewLine);
            content.Append("Sitemap: ")
                .Append("www.твой-домен.ru")
                .Append("/sitemap.xml" + Environment.NewLine);
            return File(
                Encoding.UTF8.GetBytes(content.ToString()),
                "text/plain");
        }
    }

public class SitemapNode
    {
        public string Url { get; set; }
        public DateTime? LastModified { get; set; }
        public SitemapFrequency? Frequency { get; set; }
        public double? Priority { get; set; }


        public SitemapNode(string url)
        {
            Url = url;
            Priority = null;
            Frequency = null;
            LastModified = null;
        }

        public SitemapNode(RequestContext request, object routeValues)
        {
            Url = GetUrl(request, new RouteValueDictionary(routeValues));
            Priority = null;
            Frequency = null;
            LastModified = null;
        }

        private string GetUrl(RequestContext request, RouteValueDictionary values)
        {
            var routes = RouteTable.Routes;
            var data = routes.GetVirtualPathForArea(request, values);

            if (data == null)
            {
                return null;
            }

            var baseUrl = request.HttpContext.Request.Url;
            var relativeUrl = data.VirtualPath;

            return request.HttpContext != null &&
                   (request.HttpContext.Request != null && baseUrl != null)
                ? new Uri(baseUrl, relativeUrl).AbsoluteUri
                : null;
        }
    }

    public enum SitemapFrequency
    {
        Never,
        Yearly,
        Monthly,
        Weekly,
        Daily,
        Hourly,
        Always
    }

<system.webServer>
    <modules runAllManagedModulesForAllRequests="true" />
  </system.webServer>

routes.MapRoute(
                name: "sitemap.xml",
                url: "sitemap.xml",
                defaults: new {controller = "Seo", action = "SitemapXml"}
                );

            routes.MapRoute(
                name: "robots.txt",
                url: "robots.txt",
                defaults: new {controller = "Seo", action = "RobotsText"}
                );