Access to lounge facilities at Istanbul airports?

Istanbul is served by 2 airports, Istanbul Ataturk Airport (IST) and Sabiha Gokcen International Airport (SAW).

Istanbul Ataturk Airport (IST)

There are quite a number of lounges, you can find info listed on the official website.

There doesn't appear to be any Amex lounges.

Primeclass lounges offer walk-in admission which have prices listed on this page.

More info from SleepingAirports

Sabiha Gokcen International Airport (SAW)

Lounges are listed on their Official page.

SleepingAirports lists the following information:

If you are an economy class traveller, you can enter these lounges at Istanbul Sabiha airport either by purchasing a day pass or through a membership program. Visit the individual lounge page for more details (ie. facilities, hours, pass and membership information):

• LGM Domestic CIP Lounge - Location: Domestic Terminal, Airside, upper level. Free WiFi. Hours: open 24 hours. Lounge Access: Pay at the Door (35 TL) • Priority Pass.
• LGM International CIP Lounge - Location: International Terminal, Airside, upper level. Free WiFi. Hours: open 24 hours. Lounge Access: Pay at the Door (45 TL) • Priority Pass.

Additionally, there are three member/cardholder lounges: THY CIP •Wings Lounge.

I have been to the lounge at SAW (I think it was the LGM International one, but can't be sure) and there were only couches to sit, nowhere to sleep.