Unlike walking and running, swimming doesn't allow any downtime for resting unless the dog comes out of the water, meaning they're constantly being pushed to keep moving, thus tiring them out much quicker than many other land-based exercise. See if you can find a local pond, lake, or ocean for them to swim in if they like the water enough. If they do, you might be able to train them to do dock jumping as well!
For some owners, big cities are tough places to get high-energy dogs an appropriate amount of exercise. For those with a keen eye, cities are full of agility obstacles such as picnic benches and concrete stairs that will tire a dog out quicker than a simple walk. Have them run and jump up, down, and around a series of objects in succession and create your own agility course with minimal work and free of charge!
If you're looking for a low-effort activity that will burn your dog out much quicker than it will you, grab a ball, Frisbee, or other fetch-able item, find some open space and toss away! You'll likely only tire out your arm while they're tiring out their entire bodies!
Sometimes adding a bit of extra weight can help tire a dog out quicker. After all, aren't you more tired after backpacking than after simple hiking? Get them a doggy-specific backpack they can wear comfortably and load it up with either supplies (for longer walks) such as water, food, or treats, or just some extra weight to make them work harder.