How often should babies go on outings?

My baby is 15 months old, and I'm worried we're not doing enough with him outside of the house. I try to keep him stimulated while home but I know exploring the world is important too. Are there recommendations or guidelines on how many times per week you should be taking your babies on outings? We go on walks during the week and play outside but don't do actual outings like going to play spaces except on the weekends.