How to take my WP site offline for "construction"

I have a new WP site up and running, ready to be designed and built out. That’s going to take longer than I realized (surprise surprise). I’m not publicizing the site yet, but still hate for anyone to stumble across it while it’s “under construction.”

Is there a way to take the site “off line” in some way while I build the pages, then put it back online when it’s ready?

It’s a business site with a static front page, so I guess I could write “Under Construction” but that seems lame. Is there a better way?

Tx,
WK