Can you just walk in or do we need to buy before?

For the health and safety of our staff and visitors, and to maintain social distancing, timed entry reservations are required. https://www.amnh.org/plan-your-visit

Need to reserve online first.

Need to buy early...Covid procedures.

online reservations required now to control the crowds becos of Covid

You have to buy before going in but yes you can do it very easily

You need to make a reservation before going in, but you can do it the same day.