walk on Obidos walls after 5 pm ?

There are several staircases up to the walls. I can't remember for certain but I don't recall any gates or barriers. You did mention that you are aware there is a lack of railings, but also be aware that the walkways are narrow in spots and uneven stones. I wouldn't want to do it in the dark or getting dark. A May evening should be good.

As long as it’s light outside you should be able to walk on the wall. I don’t recall seeing any gates preventing people from climbing the staircases. While there are no gates preventing and one from climbing up to the wall, there are also no railings to prevent one from falling off the stairs or walls.

There are signs at each staircase reminding people of the potential danger. For those with balance issues, they may not want to walk the wall.

In Fátima, in addition to the sanctuary, try to make it the houses of the children and the locations where Mary and the Angel of Peace appeared. Some walking is involved from where you park. The houses are a couple miles from the sanctuary.

Assuming you’re driving there is ample free parking by the sanctuary and there’s also a free lot near where Mary appeared.

Thanks for both replies!