The City of Königsberg (nowadays called Kaliningrad) with a view of the seven bridges. Image credit Historic Cities Research Project
UPDATE (2017-12-06): there's now a guest blog post on the GraphCMS blog about the GraphCMS Source plugin for GatsbyJS I mention in the talk: Gatsby & GraphCMS, Sittin in a Recursive Tree.
These are the slides of the talk I gave at the GraphQL Vienna Meetup (PDF with active hyperlinks):