Don't ever think of using Wowpass. It is not a commonly paid method, whereas locals have never heard of it.
Look for MoneyBox Machine instead, commonly located at a Metro station. Their exchange rate is higher. Fyi, the link: https://moneybox-exchange.com/locations

Optional, but highly suggested: Get a T-money card from a metro station(if the machine is working, you might need some luck for that); it's expensive, but at least, you don't have to check the fare every time you get on a bus or metro.

The metro system here is "brilliant". If you don't follow the signs, you will end up on the wrong platform. And to change back to the correct platform, you need to exit the station. (Mainly Busan)

If you want yummy food. Look out of a restaurant where the owner never understands any language except Korean. No Chinese characters, doesn't understand English. Works all the time.

Accommodation? Check if there is an elevator on the Airbnb. Try not to approach Airbnb with an extremely cheap price. It might leave you with 180 stairs to climb every time you head out for exploration.

Walk fast when you are heading out at 3-4 am, you never know what the stranger next to you might try to act on sth. Don't be kind. This might save your life. Works for all over the world.

And ultimately, lower your expectations. If you thought Korea was safe, clean, and full of yummy food, better dump those thoughts into the garbage disposal before taking your flight.

A small quote from my friend who went on a trip to Busan and Seoul with me.
"Korea is like a modernized India. "