public List<Entity> GetList()
{
     return (List<Entity>)session.CreateCriteria(typeof(Entity)).List<Entity>();
}

    abstract class NHConfig
    {
        private static Configuration cfg = null;

        public static NHibernate.Cfg.Configuration GetConfig()
        {
            if (cfg == null)
            {
                cfg = new Configuration();
                cfg.AddAssembly("catibll");
                cfg.SetProperty("connection.connection_string", ProjectSettings.Current.ConnectionString());
            }

            return cfg;
        }
    }

    abstract public class NHFactory
    {
        private static NHibernate.ISessionFactory factory = null;

        public static NHibernate.ISessionFactory GetFactory()
        {
            if (factory == null)
            {
                factory = NHConfig.GetConfig().BuildSessionFactory();
            }

            return factory;
        } 
    }

session = NHFactory.GetFactory().OpenSession();