National Stadium

Are we able to visit inside as I saw admission fees, even without events? Also from above as written, "* CNY140 for Through Tickets of Beijing Landmark Tour, including the National Stadium, the National Aquatics Center, the National Centre for Performing Arts and the CCTV Tower; the ticket is valid for one month," anyone can help where I can purchase this? Also for National Centre for Performing Arts, are we able to visit inside?