There is certainly a BA lounge. It is an OK lounge, but gets busy with all the shuttle flights to London. All the usual stuff, bars, nibbles etc. Access is by stairs or lift from the BA departure area. The lounge is basically a circular mezzanine level.
There is a TV lounge, but last time I was there it was closed.
I am not sure about showers etc. but I guess they are there somewhere.
I have used the lounge for BA and Finnair OW flights, I am not sure if there is a more convienient lounge for other OW carriers.
Nick