Airport lounges are the gilded uplands of air travel, refuges of calm, quiet and comfort where the food and drink are free, the seating well padded and the loudest noise is the hiss of the espresso machine. If you're travelling in premium class you're in, but for economy flyers, pay-for-use lounges are one option, offering respite when and if you need it.
Plaza Premium lounges are located in 160 airports in 44 international airports across the world. Most of those are in Asia and the Middle East, plus Sydney, Melbourne and Brisbane. Coverage in Europe and North America is thin. The Plaza Premium Lounge in Hong Kong costs $US75 ($A110) for two hours, $US100 for five hours. The Plaza Premium lounge at New Delhi's Indira Gandhi International Airport is a much better deal, at $US31 for two hours. In Dubai, Plaza Premium clients use the Ahlan Business Class Lounge in Terminal 1, which costs $US61 for three hours.
Whether a lounge is worth it or not depends a lot on the airport, how long you're in for and what you're getting for your money. In a great airport like Singapore's Changi, it's questionable. However there are no other airports like Changi. If you're stuck in one of those for a couple of hours or more, a calm lounge with a decent food and drink selection, fast internet and showers is going to make a difference to how you feel at the other end, but check reviews on TripAdvisor, standards and amenities vary wildly.