One can take the bus to Sokcho from the Gangneung Express Bus Terminal. As of April 2007, a bus leaves Sokcho every 30 mins and the trip lasts for an hour and 20 mins. The ride is quiet comfy though there's not much to see along the way.
I was plesantly surprised to find a bus that leaves from Southern Ulsan to Northern Sokcho. It only cost me about US$25 or so to make that long 7 hour journey.
Take note that you'll need to change buses at GangNeung though. I wasn't aware of it till the last minute - Thank God there was a kind bus driver who looked out for me. He pratically carried my bag and guided me to the next waiting bus.
The bus leaves Ulsan Inter-city Bus Terminal at 10.30am sharp.
You can take number 7 for seorak mountain.There is a bus from sokcho-city to seorak mountain. It takes 20min to Mt,seorak.