Well... you're well under-exposed which is the basic problem. Experience is the best teacher and you wont make that mistake again.
When you've made the effort to climb all the way up there, then if in doubt do the time honoured thing and bracket like ****!! :lol:
The bracketing feature on your camera will be useful depending how much it under and over exposes either side of the metered setting. If it's only a 1/3 or 1/2 stop either way I doubt it would have been much use here as you could be a good couple of stops under exposed. That was no doubt a very airy light and atmospheric place which has well and truly 'fooled' your camera meter.
It's worth investigating if you can adjust the exposure bracketing though.