On the level of difficulty of different bike tours

Finding the Right Bike Tour for You

The only way to ascertain whether or not a bike vacation tour is your speed is to read a detailed description of each day’s route. Although most touring companies offer longer routes as an option, this doesn’t mean anything if everyone else chooses the shorter option. Strong riders who end up on tours with less experienced cyclists can miss out on anticipated challenges. This isn’t satisfying.

There are a few variables that determine the difficulty of the ride.  One key one, distance, depends on the specific tour you book, so you’ll have to ask.  
The majority of guided bike tour companies classify beginner trips as those that around 30 miles a day along mostly flat terrain. Intermediate tours are usually 35-40 miles per day, and may include some hills. More challenging bike tours for recreational riders may consist of trips over 45 miles per day with major hills included.  And then there are very challenging/pro level tours for those in top shape.
Editor’s Note: An option for those who are on an easier tour than their level is to ask the guides to run an extra ride for you.  This is no problem with the higher end companies.  I took my wife to Bordeaux with DuVine Adventures.  Bordeaux is very flat, which was ideal for her.  To get extra mileage in, one of the guides took me out every day and found some good hills.  This was actually extra satisfying as the guide was a local from Bordeaux, and knew some good hills, as long hidden beautiful spots.  You can always go out and ride yourself, but it’s safer with the guide.
See our Destinations Guide for Details on all of these locations:
Easy - Flat
France: Bordeaux, Burgundy, Champagne, Loire 
Cape Cod
Moderate - Rolling hills
Italy: Tuscany / Sicily
Basque Country
For serious bikers, there are tours that challenge you to the core.  For those looking to take a step up in Europe, hilly Tuscany and Piedmont, the Swiss and French Alps, and the Pyrenees are a good choice.   The Colorado Rockies is also a good choice for a challenge.  We've done a write-up on how to plan a tour to ride the mountains of Europe.  Another option is to follow one of the three Grand Tours of Europe, and ride a few of the challenging stages that the pros do.  On many of these, a pro will join you!  
Here are a few more of our favorite options: 
Hawaiian volcano
Canadian Rockies
Colorado Rockies
Following the Pro tours
Again, see our Destinations Guide for Details on all of these locations.