Leadership dedicates certain "open door" hours each week for any team members to reach out regarding any topic. Send a calendar invite to all employees, so they're reminded when these hours are occuring.
Open door hours are meant to replace 'swinging by someone's desk' in the office to ask a question or just for a quick chat.
These small conversations are important for bonding, because they're less formal than appointments. They also make sure employees feel comfortable reaching out to the leaders they don't have scheduled appointments with, and allow spontaneous networking to still happen!