I run https://www.daysoftheyear.com, a calendar website which lists all of the weird, funny, odd etc national days, holidays events. Alternative celebrations, like 'Ferris Wheel Day' on Feb 14th (vs Valentines Day). They're all real celebrations researched, described, etc. It was built (and rebuilt several times, and constantly iterated) by me, from scratch, on WordPress, in my spare time over a period of years.

The site generates >$1.5k per month at the moment from AdSense alone, without any marketing other than SEO and broadcasting to the social followers we've accumulated. This revenue is secondary to the real and long-term value being generated in the form of large numbers of membership/email subscriptions and social followers.