I understand car rental GPS systems allow inputting a phone number instead of the address to look up a driving route. For Jeju, since a lot of the attractions are nature-oriented and may not have a phone number, how would this work?

English GPS systems seem to be a rare commodity from the car rental agencies, so I'm looking for an easy way to find my way around driving without being held back by the language barrier. I don't know how to input an address in Korean, so the phone number method is crucial. The places I would like to visit include :

Manjanggul Cave
Seongsan Ilchulbong Peak
Cheonjiyeon Falls
Oedolgae Rock
Jusangjeolli Cliff
Cheonjeyeon Falls (Yeomiji Botanical Garden)
Yongduam Rock
Sanbangsan
Sangumburi Crater (산굼부리)
Hallim Park (Ssangyonggul and Hyeopjaegul Caves)
Songaksan Mountain