Meydenbauer Center is just west of I-405, near the middle of Bellevue. The address is 11100 NE 6th St. Bellevue, WA 98004.
Coming from Seattle, you will want to either take Hwy 520 to southbound I-405, or Hwy 90 to northbound I-405.
Heading South on I-405
Don't get in the two-lane exit for NE 8th St; continue to exit 13A, to NE 4th. Exit right onto 4th, then take the first right turn on to 112th, then the next left, onto NE 6th St. The underground garage entrance will be immediately on your right, as shown below.
Heading North on I-405
Take exit 13B on your right to NE 4th St where you will turn left and cross over the highway. Take the first right (112th Ave NE), then the next left (NE 6th St). The underground garage entrance will be immediately on your right, as shown below.
The entrance to the garage looks like this (Note the 6'9" clearance).