It's a little hard to see unless you know where it is. The signage is subtle and (I think) it's in a building along with one or two other businesses. Check the map that the owners posted the link to. and you can also go to google maps and zoom in to the spot using satellite view to se a real life image of the spot.
if you were headed away from Cortecito towards the airport, it's on the main road Av. Barcelo, just past the intersection with Av. Alemania (the el Dorado corner). it's about 2 "blocks" past the intersection, where the road starts to twist a little. Go slowly.. it's on the right hand side. Also, I think there's an old thread on the forum that has some pics of the outside... and IIRC there's a pic of the sign, so that you'll know what you're looking for.
once you find it you'll slap the side of your head and say "how did I miss it before!!!???"