Pilgrim's Progress

 is a shop in Sky Barnet. It is the only shop in the Blue Kingdom where Locomotives can be traded.

Unlike other shops, locomotives cannot be bought or sold. As you must always have a locomotive, you may only trade in your current vessel for another one. Depending on the values of each locomotive, you will gain or lose Sovereigns when you trade it. The shop interface will display how many Sovereigns you will gain or lose if you traded for each listed locomotive.

This is calculated according to each locomotive's value. For example, if you currently have the Bedivere-Class Escort, worth 1500, and choose to trade it in for a Parsival-Class Courser worth  500, you will gain  1000 along with your new locomotive.

If however you want to swap a Parsival-Class Courser for a Bedivere-Class Escort, it will cost you 1000 to do so.