There are many different ways to travel around Jorvik and give your horse some rest. The most popular option is the horse trailer that can take you to almost all the places in Jorvik that you have already unlocked. The horse trailers can be found in most major cities and villages and a few other places - you can’t miss them! Just hop on, choose the place you want to go to in the list, and you’ll be there in the blink of an eye, in exchange for Jorvik Shillings.
To unlock a horse trailer for a location, you need to have visited the place on foot first, and some locations also require you to finish the introduction quests.
If you want to travel on water instead, you can use one of the ferries that you can find in Fort Pinta, for example. Please note that you will need to have unlocked both sides of the ferry to use them. (You can unlock the ferry by riding to the ferry landing and clicking on it.)