We have had success in transporting our bikes on our trips to Europe in large cardboard bike boxes flying in and out of the same airport for our tours.    We book the same hotel at the beginning and end of each tour.  Dimensions of the current boxes we are using for our upcoming tour in September are 34”x62”x 10”.  For one of these boxes this will be its 4th overseas return trip.    These are very sturdy boxes made of thick cardboard.   We remove the pedals, turn the handlebars, and remove the front wheel and strap  it to the frame.  Helmets, shoes, one pannier and clothing etc. are stored in the bike boxes providing additional protection.  This leaves us with one pannier each as a carry on eliminating the possibility of losing any luggage.   We place AirTags in the bike boxes. We have never had any damage to our bikes using these sturdy cardboard boxes which we reinforce with packing or duct tape as necessary. 

We flew into Frankfurt for our first 4 tours staying at the Sheraton Airport Hotel which stored our boxes for the 7 or 8 weeks at no charge.   We will be flying into Zurich next week for the 3rd time.   We store our bikes at our hotel near the Zurich airport with convenient shuttle service to and from the airport.  We have also flown into Lisbon and Barcelona.  The hotel in Lisbon also stored our bike boxes at no charge.   Our small hotel in Barcelona had no storage facilities for our boxes but we managed to store them for a small fee in a nearby partner hotel under renovation.

What a goal mine of information for those of us following in your tire tracks. I especially love lodging names. Did the Frankfurt Sheraton have a shuttle? 

Edit - I went to your journal. I see the Sheraton was so close to Air Canada that you could walk over. What luck!

Barcelona is our projected end point. I found your journal info for that day. Again, loving all of the details. They are so helpful when planning.

Hi Kelly - I am glad my comments were helpful.    The Sheraton Airport Hotel is easily accessed directly from the terminal by crossing the street and using an elevator.   We rode our bikes directly from airport.   Our first attempt was a comedy of errors getting out of the airport - all it took was one wrong turn.  There is a good route through the forest to the bike path along the Main River.  I can send you a screen shot of the route if you like. 
My email is kclassen@shaw.ca.