South Korea has almost two dozen national parks, many of which are free to enter. If you borrow hiking gear for free from the Seoul Hiking Tourism Center, you won’t pay a cent.
You can also go on free guided walks in the capital city, ride public transportation all around for almost nothing – even into the cute suburbs that surround it – and enjoy street food on a dime.
Add gardens, universities, and oceanside walks around the country, and you’ve got yourself a full itinerary for little to no cost.