If you live near a large body of water, it might be fun to rent a boat, any kind, and take your dog out on the water. If your dog is a fan of water or just relaxing with you, then this could be a fun afternoon spent together. Just make sure your dog doesn't try and jump overboard.
There are many advantages of going to the beach. You can get out of the house and have a blast. Just be sure that your dog is allowed on the beach. You can let them off the leash and play fetch, or tug of war. You could even go out for some ice cream. Who knows? Your dog might love frolicking in the waves. All in all, a day at the beach sounds like a good idea.