There is a ledge nearby, but you will be standing allot before entering, and you will have a bunch of walking to get through all of the exhibits. I would definitely get a wheelchair.
If you can't walk or stand too long I highly recommend that you get a wheelchair. Sometimes there are large gaps btwn seating areas and/or they are already taken. I believe you can only get a wheelchair if you have someone to push you around. No electric scooters.
Yes, the museum has plenty benches and comfy chairs spread around. There's even a comfort area with a relaxation fountain for you to calm down after the first three floors dealing with slavery, Emmett Till, and the civil rights movement. There are also wheelchairs available. My stepfather used one for the whole tour.
Yes they do have several places for you to sit and rest, if you need to.
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