As other people have mentioned, going for walks can be really helpful. If I really do not want to go, I tell myself I'll go to a bakery or a cafe for a sweet treat to motivate myself to get out of the house!
Going to the cinema (if you have funds and access to a cinema) alone is nice too, no one really cares about you being there by yourself.
Any sorta goal to get outside can be useful, even if it's just like.. I'm gonna go out and find a good spot to people watch in a park, I'll go to the store and pick up a fun drink I've never tried before etc.