I was at Obelisk a few times. I specially liked the jacuzzi on the roof. The problem I thought was that it was spread over ten small floors and therefore you could spend quite a time hiking up and down the stairs. It did have one tiny lift that could squeeze in about 4 people. But if you were on a lower floor and just missed it to get up to the top, you might have had to wait 4 or 5 minutes to be able to access it for it seemed to stop at every floor.
In addition to Obelisk, there were other saunas before Babylon opened. I have memories of Volt which I believe was one of the first. It was located off Asoke in a soi to the left as you went up towards Rama 9. I enjoyed a few visits there. There was another on the right at the end of a small one-way soi off Ploenchit just before you came to Soi Chidlom. It only lasted a couple of years or so.
When the original Babylon opened it was a revelation. The owner was clearly rich for to the left of the entrance was a large glass-fronted cabinet with antiques. At week-ends there would always be queues at reception, mostly of youngish Thai guys because not many farang had discovered it in its first 2 or 3 years. In addition, on the left there was a waiting room with chairs - also full. As it became more popular, the owner added an additional section to the right with more cabins, yet another staircase which led down to a small coffee shop. This was in addition to the main restaurant above the reception area. A nice touch was that at weekends there would often be a guitarist or flautist playing quiet music.
Not many seemed to be aware that on the left as you entered the restaurant there was a closed in area. This was actually a massage room with a decent sized bed. I recall it was looked after by the sweetest guy named Gung. Although it was a sauna with so much free sex, I happily found myself in the arms of Gung a few times!
Was there any more enjoyable time than sitting with a drink in the open air at one of the bar tables on the top floor with a parade of gorgeous Thai boys in towels constantly drifting past? At the southern end of the balcony area was a series of large showers and many of the lads had not dried themselves properly, droplets of water still glistening on their smooth bodies!