My girlfriend and I stayed in the "Golden Lion Inn" for 3 nights in July. For our first visit to Madrid, we planned on staying in a quality hotel and based on the reviews we picked this one – our room was on the first floor and facing the street, Calle Cava Baja. First of all, the location and surroundings are great – it's located in the lively La Latina part of the city which is pulsating, especially after siesta. The hubbub on the street (and inside the hotel's "enotaberna" as well) was quite loud, but the balcony door and thick curtains kept the noise away pretty well, i.e. it wasn't disturbing our sleep. Same goes for the noise from the hotel's bar: it's loud downstairs, but the room we stayed in had a separate door which kept the noise away.
Secondly, our room, "Cava", was very nice and sleek! The pictures on the hotel's website do lie a bit due to the wide-angle lens used, but still, we weren't disappointed or upset about it. The bed and pillows were great – they're made of some sort of memory-foam. I can't remember when I've had such deep sleep. The bathroom was very pleasing as well: modern and high-quality (Grohe rainshower :3 ). Also, those wanting to watch TV during their trips, the large Sony HD TV didn't include an international news channel as promised. Didn't ruin our trip though.
The biggest complaint is that the room air conditioning was somehow broken in so that you couldn't yourself control it but you had to go downstairs to the reception to ask them to turn it on (and off when it got too cold). Quite tiresome. I hope they fix this soon.
The reception and restaurant personnel were, apart from every other Spaniard we met, capable of communicating in English and very amiable! The breakfast was delicious although confusing at first, as you had to separately order your caffe con leche and scrambled eggs with bacon. It was nice though, served tailor-made for you ;) . The restaurant interior with its glass floor was spectacular as well.
All in all, I very much would like to give Posada del León de Oro full 5/5, but due to the AC issue, I'm forced to present it with 4/5. DO NOTICE HOWEVER that this place fulfilled our expectations, was very pretty and tidy, had very good service, and a nice bar and restaurant. Definitely a would-visit-again hotel.