The Black Kirk:
The Black Kirk is a very eerie place not just watching Outlander but especially being at the location. It also feels like it's a place set to honour those who lie there.
The Black Kirk is in fact not very far away at all to Culross. We saw The Black Kirk featured in Outlander when Thamas Braxton became ill and was at deaths door.
Claire was desperate to prove he was poisoned and not "possessed" as The Father was wanting to insist.
In order to change Thamas's fate Claire and Jaime go to The Black Kirk to locate the plant he may have eaten resulting in poisoning. This was also an opportunity for Jaime and Claire to become better acquainted.
We learn a bit about Jaime's past education and the mischief he and the boys would get up to whilst they played at the site.