Believe it or not, there are plenty of restaurants out there that allow dogs. Find one in your city, check out any regulations or restrictions, and head on over there. You get to enjoy a nice meal, maybe bring your dog's food or snacks, and take in some new surroundings.
If you can, consider taking your dog to work every now and then. Since your dog is calm, there won't be chaos in the office as a result. But you will expose your dog to new people and a new environment, which could be great. The newness of it all is exciting, providing new things to sniff and explore. Plus, you get to go home together later, and your dog can recharge their batteries after a long day of being social.
Believe it or not, this is a great idea, especially if you play anything animal related, like Planet Earth, or any animal channels like Animal Planet. Even YouTube videos work. Normally people do this for cats, but if your dog is super calm, and only seems to get excited when there's something new, interesting and fast to watch, then this is a great way to provide entertainment.