Maps and accommodation

Naver map is must to efficiently move around. Google maps doesn't provide driving directions, only public transportation. There are also tourist trails with photos similar to street view on the main treks.
There is even more in the Naver maps if you let Google translate it for you on the web, but to book an accommodation or order a taxi, you'd need to have a local ID, so for most it's probably just to survey prices.

Mapy.cz are best offline for trekking.

General info

Check more info for getting around Korea.