Especially when you’re doing research.
Some of the odder and/or more interesting (and even sometimes useful) places I’ve found in the course of doing research for different projects:
A page for converting dates to and from the French Revolutionary Calendar. (If you’re curious, today is Décade I, Decadi de Brumaire de l’Année CCXXI de la Revolution.)
One of many online date-of-Easter calculators, in case you want to know what date Easter is going to fall on in the year 2525. (April 15th, by the Gregorian calendar, for the Western churches.)
An on-line text of Mrs. Beeton’s Book of Household Management.
No wonder research is so dangerous . . . you can fall into it and never come out.