This nonprofit foundation, 2km inland from Hat Mai Khao, protects hundreds of cats and dogs (many rescued from the illegal dog-meat trade), focusing on sterilisation, castration, rehoming and animal-welfare awareness. Visits are by in-depth tour. The 'old dogs' enclosure can be upsetting, but it's a happy home. Visitors can play with the animals, or become dog-walking, long-term or animal-transfer volunteers.
At the time of writing, Soi Dog is home to 850 dogs and 150 cats, many of which are adopted to Europe and North America. It's signposted from Hwy 402 just north of the airport.