First off if you don't know anything about Jeju Island it's totally ok. I didn't know a single thing about it before landing in Korea. Jeju is actually on the New 7 Wonders of the Nature and is a hot honeymoon destination spot in Korea. It is even called 'the Hawaii of Korea'.
If you are in Seoul or Busan flights are really inexpensive. There are also many ferries that go to Jeju but I was warned not to take them because it is a long travel time and not nice quarters. I am awful about planning before hand and booked my flight literally 12 hours before I left and still only paid $100 roundtrip. I flew on Jeju Air and had a great experience but many other airlines fly to Jeju as well.
If you are flying in from another country book 2 flights - One to Seoul/Busan and then one to Jeju. Booking a direct flight from elsewhere is WAY too expensive.
Getting around the island
The great news is Jeju has an amazing bus system that will take you all around the island. I was so happy to find that the public bus system is not only extensive and cheap but also easy to navigate and reliable. The bus system covers all of the major sites and hiking trails. I found the drivers and ticket agents barely spoke english but even when I completely butchered the name of a sight (seriously try and say this word - Cheonjiyeon - it is physically impossible) they knew immediately which ticket I needed. There are bus stops all around the island and a main bus terminal near the airport. For reference on how cheap the bus system is: A bus to the opposite side of the island (about a 2 hour ride) costs me $3. And yes your T-money card works here also.
You can also use taxi's to get from scenic spot to scenic spot very easily. There are many driving around and taking them is safe. Again I butchered names of the places (or showed them on a map) and they easily took me there.
where to stay on the island
Cheap and convenient for bus travel:
Because of the great bus system I chose to stay as close as possible to the Jeju Intercity Bus Terminal. I knew I would be using the bus to go everywhere and wanted to see sights all over the island instead of just in one specific region. It worked out perfect, my walk each morning to the bus terminal was less than 5 minutes.
Las Vegas Style Hotels:
In Seogwipo-si (the southern region) of the island are the expensive (but for good reason) hotels. I am talking crazy Las Vegas style hotels with restaurants inside of windmills, crazy huge swimming pools and 24 hour casinos. These are where all the honeymooners are but it is also a good place to stay to easily reach the best waterfalls.
Top things to see in Jeju
Jeju is on the 7 wonders of the world list for nature and for good reason. Such a small island has some of the most beautiful things I have ever seen!!
The crown jewel of Jeju and one of the most photographed lakes in the world that resides in the peak of the mountain. It is the highest mountain in South Korea and the whole mountain is a national park which makes for incredible views.
Important to know: a hike to the top takes all day. So unfortunately if you have little time in Jeju this will take up one full day of your trip and requires waking up early. For a full guide on how to climb Hallasan click here.
The most famous (and my favorite) waterfall on the island. It is 23m high and increbibly close to the ocean. It is also the most crowded so I would hit this waterfall first thing in the morning.
The stairs down to the waterfall are wooden and very well maintained. But it is a steep climb back out to the main road.
$2 to enter
The second most visited waterfall on Jeju Island. Local legend says that this waterfall grants wishes and many newlyweds visit it to wish their new marriage luck. This legend comes from locals praying for rain here during droughts and the gods answering every time.
To reach the waterfall follow the (very large and well maintained) paths and bridges.
$2 to enter
Rugged cliffs that formed from volcanic pillars of rock. Similar to Giants Causeway in Ireland. A National Monument and UNESCO world heritage site.
$2 to enter
Sunrise Peak or Seongsan Ilchulbong
Archetypal tuff cone the was formed by volcanic eruptions on the shallow seabed about 5 thousand years ago. A very steep walk to the top consisting of staircases.
$2 to enter
Jeju has fantastic trails that encompass the entire island following the coast. I found trail number 7/8 to be beyond beautiful. There are 17 trails in all.