gistfile1.cs

using System;
using System.Linq;
using System.Xml.Linq;

namespace ExampleConsoleApp
{
    class Program
    {
        static void Main(string[] args)
        {
            const string xml = "<weather><temperature>30C</temperature><foo>bar</foo></weather>";
            var xdoc = XDocument.Parse(xml);
            var temperature = xdoc.Descendants().Single(d => d.Name == "temperature").Value;
            Console.WriteLine(temperature);
        }
    }
}