Okay this sounds basic, particularly as the weather warms up around the country, but I will have to repost this in January! Yes, take your baby for a walk throughout all the seasons. My son was born in January – if I waited for Spring that would have been 4-5 months inside! With a newborn! All day! Every day!
Instead, we bundled up and walked and walked and walked . . . every day. Even if baby is bundled up and the cover is over the stroller, the air is still different, the sounds are different, and the motion is different from indoor activities. This is a great time for you to point out some things, “Do you hear a bird?” “Do you hear a car?” “That is a stop sign.” “That is a fire hydrant.” “Do you see the dog?”
Naturally, in the nicer weather your baby will see more, probably hear more, and that fresh air always makes for some great naps!