Tickets for the Water Cube are bought (for ¥30) from booths off the northwest corner of the building, and it is entered from the east. It's open 8.30-4.30 at weekends and 8.30-6 on weekdays, but if there are events on (shows, not sport--these buildings are all white elephants) then access may be cancelled. Don't bother asking your concierge as he'll have no idea, but take pot luck.
Although otherwise there's nothing much to see inside, to view the light filtering through the bubbles is worthwhile. Entering the Bird's Nest is another matter. The ticket office is by entrance D and access through entrance E, open 9–6, ¥50. The main impact of this building is from the outside. It would be worth buying a ticket if access was allowed to the passages and stairways within the mesh of girders, but you're only permitted to go straight through to the pitch, at which point you might just as well be in any other middling size stadium.
In general the space has little to do with real Beijing, and during the week has the feeling of an ultra-modern ghost town (but avoid weekends unless you want to spend a long time lining up for tickets). Other sights include the Data Centre (think filtering and censorship) which is a mixture of giant silicon chip and circuit board; a retro TV tower; and the metro station itself, full of cod traditional Beijing themes including a wall made of siheyuan roof tiles, and quite possibly the planet's most arty.
For an antidote get off at Beitucheng on your way back, currently the southern terminus of Line 8, and take a walk along the remnants of the Yuan dynasty city wall.
Peter N-H
China