Basically the title. The fact that we can read an encyclopedia entry on the economic history of the Netherlands from our phone is crazy. Scrolling over to a random island in the middle of the Atlantic to experience a virtual street tour is insane. There are even websites that let you see live security camera footage (shoutout to EarthCamTV). We have so much information that we take for granted.
As someone who routinely edits on Wikimedia projects, I think the average person doesn't fully comprehend both how ungodly expansive Wikipedia and its sister projects currently are and especially how ungodly, unfathomably incomplete it still is. Let's say you're a person who lives for about 41 million minutes (~78.5 years). The English Wikipedia currently has 6.895 million articles, meaning if you started reading Wikipedia (just the articles; nothing else) from birth until the day you die with absolutely no breaks, you would have about 6 minutes per article to complete it. However, the English Wikipedia isn't the only one; the English, Chinese, Arabic, Egyptian Arabic, Farsi, Polish, Spanish, Portuguese, German, Swedish, Cebuano, Ukrainian, Winaray, Vietnamese, Dutch, French, Italian, and Russian Wikipedias all have over 1 million articles, and there are dozens of other, smaller Wikipedias. Non-English Wikipedias often have regional content that the English Wikipedia simply doesn't because of language and cultural barriers.
If that weren't enough, Wikipedia has the sister projects Wiktionary (an everything-to-[language] dictionary; e.g. the English Wiktionary with 8.2 million entries is everything-to-English), Wikimedia Commons (an interlanguage repository housing over 110 million pieces of copyleft media, including images, videos, documents, audio, map and tabular data, and 3D structures), Wikiquote (a repository for quotes from famous people and media), Wikidata (a very extensive database), Wikisource (a repository of transcribed freely licensed texts), Wikispecies (a taxonomy catalogue), Wikinews (original reporting; English one is mostly defunct now), Wikibooks (user-created books), Wikiversity (user-created lesson plans; I don't really hear much about it), and Wikivoyage (a travel guide for anywhere in the world). There's also now an in-development project called Wikifunctions for code.
As if that weren't enough, the English Wikipedia alone is woefully incomplete compared to what it could be. There are millions of articles with tons of potential just waiting for a user to come along and dramatically expand and improve them (and in many cases, even just create them in the first place). As an example, there's an editor whose main focus is New York City architecture, and because of them, I would say that Wikipedia is the best single source in the world for learning about it. There are countless other subjects, however, which don't get that same treatment. Featured articles – understood to represent the best Wikipedia has to offer – comprise just 0.09% of the articles. Obviously not every subject has enough coverage in reliable, secondary sources to become a FA, but there's still so much untapped potential.