I've not been cycling nearly as much in Seoul as I used to in Gwangju, but I'm trying to make a bit more of an effort. I've started making a few routes. This is my local:
It's about 15km and has about 392 metres of elevation. One of the hills is brutal, from the back of the military base up to Haebangchon Ogeori (5-way junction).
You set off south to Noksapyeong station, then head west towards Samgakji. From there you head north and loop around the military base to the back of Haebangchon. This is where the beast of an uphill starts. Once you get to Haebangchon Ogeori, head onto the Namsan ring road and go clockwise round towards Chungmuro. From there you head up past Dongguk University until you get to the entrance of Namsan Park. Here you will start a 2km climb to the top of Namsan. Once you're up and over Namsan you'll end up back on the ring road. Take a left and head anti-clockwise until you end back in Haebangchon.
This isn't a ridiculously hard ride, but it will test you. There's quite a bit of elevation for such a short ride. There's a lot of nice cruising down mellow inclines so it's not all gloom!
I will be rocking this route most mornings from now on.