Great engineering story. Wanted to add office space without ruining the outside look of the grounds.  They dug a huge hole, built the addition plus 2 story parking garage then covered it up. Only things you see outside are the skylights, a small building housing the elevator and the upside down rotunda.

First is picture of outside of back.

Following pictures are the underground stuff.

They also built a rotunda outside that is a replica of the Capital dome---except it is upside down. Not a great shot, but only one I have.

For good photos and history check out

www.thc.state.tx.us/travel/statecapitol.html