Red ,,
I got pissed off earlier on such a random question ,, calmed down I will explain, for I also see benefit for others coming to Seoul.
First of all ,, the Google is your best friend. Also many mentions of hotels and motels in the earlier posts FYI.
There are three major business districts in Seoul.

Downtown, by the city hall,, mostly financial ,, news corp and diplomatic.
Yoido Island, in the middle of Han River ,, Finance and insurance.
Gang Nam ,, hi-tech, e-commerce and fashion. A city of 15 million people ,, larger than London. Also many of these business intertwine in various districts. In fact the whole city is a huge business district.
Ask your friend where he is.

Also two types of bath houses ,,
Sauna - bath house (목욕탕), it is found in every neighbourhood ,, simply ask for sauna ,, and scrub (때밀이) .. three types of tub (Hot, Med Hot, Ice Cold) ,, two types of Sauna (Steam and Dry). Do a due diligence ,, there is a Korean bath houses now in every major cities in the USA, Canada, Australia and UK.
https://www.google.co.kr/search?q=ko...83%95&tbm=isch
Always take the shower first with soap, before entering the tub.

Then there is Jjim Jil Bang ,,, notice double J (찜질방) ,, these have special special earthen cavern, on top of all the tubs and are huge ,, where both men and women go into the cavern,, wearing shorts and shirts provided by the establishment. This is an all day affair. You sleep ,, eat , sauna,, sweat ,, scrub,, lay around and open 24 hours. In fact ,, for some of you riding Korea,,, can go in at all hours,,stay over night for USD 8 + scrub fee of USD 15 (scrub not required,, every one sleeps in a big hall, on a mat) ,, tooth brush,, razors (a buck each) ,,you have own secure locker. One or two good ones in every city. I have done this several times,, when riding till midnight.
https://www.google.co.kr/search?q=ko...B0%A9&tbm=isch

All the hotels and motels have secure and covered parking. Every single one ,, since customers need to hide their license plates.