Sometimes indoor spaces are the best places to teach a dog a new trick. There's usually less outside stimuli, and therefore, more concentration for the task at hand. Use your time inside to work on improving their manners, behavior or ability. If you're lucky, it may also tire them out mentally or physically in the process!
One of the hardest parts of being stuck indoors is the general lack of exercise space, which can be tough, especially for larger dogs with higher energy drives. Take advantage of your space by using staircases as play or exercise areas for them to ascend and descend. It takes a lot more effort than running, will improve their coordination and may help settle them down when there's no place for them to truly run.
If you don't get much one-on-one time with your dog or even if you do and just thoroughly enjoy it, take advantage while it's inopportune to be outside. Grab your pup and cuddle up on the bed or sofa with some TV or movies.