+1

Doesn't even have to be a zip up bag. If you can attach a shoulder strap to the bike to carry it - all you need is a cover that slides down over the strap and hides the fact that it's a bike attached.

I was once refused entry to The Van Gogh Museum in Amsterdam by the door b!tch because I had an unconcealed Brompton.

"No- it is forbidden to take the bike in"
"But - I just want to check it in to the luggage room"
"No - it is forbidden to take the bike in"
"I'm not going to ride it up and down the galleries - I just want to check it in"
"No - it is forbidden to take the bike in"

I have been back with family but without the bike since - but I'm still plagued by a burning desire to return with the big hidden inside its bag just for the hell of it. The building has a big central spiral ramp. Hmmmm