I've never been up Tower Bridge before because, like everything in London, the trip to the top is probably extortionate and rammed with people. Early in the morning with no tourists and just the early City workers walking to work its actually quite peaceful, an old lift takes you up to the walkways and a newly installed glass floor offers a view of the bridge and river below. Finger crossing did not have a positive effect on the weather but despite it being an overcast day the views were still amazing - I've lived in this city for too long (nearly nine years) but the views still make me happy and seeing the river stretched out in front and below me and seeing London life reduced to toy-town size was pretty magical.
The glass floor area is actually pretty small and in the class I attended there wasn't room for everyone on it - it's a bit of a shame how everything in London feels like an attempt to rinse money from you (the class was £25 so I felt like I was paying a £10 premium for location and novelty). Why not just sell a few less tickets to make it slightly less cramped? (Tip - arrive early, earlier than recommended on the ticket...) I spent the first part of my practice terrified of accidentally whacking the person next to me but once I'd got over my initial annoyance I did really enjoy the class. The yoga instructor was great - as an aspiring yoga teacher myself these type of classes must be the hardest to teach as you'll get a mix of experienced yogis and complete novices just there for the view or dragged along by a friend.
The 45 minute class went through gentle early morning stretching and sun salutation sequences - very appropriate given the setting! There were plenty of opportunities to enjoy the view while in standing or floor-based poses. I'd recommend a pair of gripp-y yoga socks (I have these) for working on the glass floor as using a mat will block the best part of the view (mats are provided anyway so no need to bring your own). While the yoga was beginner level, I think you'd enjoy this more if you've been to a few yoga classes or at least done some YouTube videos and are familiar with the key asanas and some "yoga speak".
The website doesn't currently appear to be offering any more of these classes but I'd recommend checking back soon if you're interested.
I've booked Sky High Yoga at 20 Fenchurch Street for next month for a bargain £10 (feel like thi is cheap by London standards for even a regular yoga class) and I'd love to do Yoga at the Shard but it's maybe one for a birthday present (hint hint) as its a little pricey...