From the outside it looks like a modern, trendy, cool, funky bar, which is right beside the entrance to Embankment tube. When you go in you're met by the upstairs (ground level) bar which is, to be honest, a bit narrow and uninviting.
Head downstairs, where you'll be amazed to see that the bar stretches out before you. The decor is lush, with plenty of comfy seats and couches, and great soundtrack every night. They also specialize in cocktails, which aren't cheap at £5 a throw, but are great fun.
The bar stays open until 3am every night from Monday to Saturday, and couldn't be closer to the tube. I would definitely recommend it for a quick drink before heading on somewhere else (its free after all) but bear in mind, like everywhere in the West End, it gets really busy on the weekend.
Have a look at it on their website here.