https://www.deephollowranch.com/how-far-can-a-horse-travel-in-a-day/

An average horse in good condition can travel roughly 25-35 miles in a day with appropriate food, water, and ideal conditions.

Galloping at top speed (25-30 miles per hour) an average horse will only last about two miles. At a trot (8 to 12 miles) a horse will last for 20 miles before it tires out and needs rest.

These numbers can give an idea about travel, sending messages, and governing large empires in ancient times.

The imagery of exploration and sea travel was a popular subject in the literature of the Elizabethan-Jacobean era. It was the Age of Discovery, and John Donne himself also had experience in sea travel. The heroic adventure stories of the people who fulfilled the Renaissance curiosity through their expedition were fascinating enough to stir the imagination of the writers of the time.

Exploration is a process of understanding a wider world, but Speaker is no more interested in it since he has already found the perfect world in his little room with his lover.