A "must see" during your stay in Beijing, allow a full day for the trip. There are a number of points that you can visit the wall, from Badling, the nearest and most accessible point but also the most redeveloped and "touristy", to Simatai and Jinshanling, much further away but also less developed and more authentic. It's worth hiring a cab for the day for the trip - either your hotel can arrange, or you could negotiate with a random cab driver.