Riddle of the Day
Rate itOne hand-picked logic or maths riddle a day, with a hint and a full solution.
Every day: One logic or maths riddle a day, the same for everyone and dated on the front page (Monday, October 5, 2026: Missionaries and cannibals), with a level from 1 to 5, an answer box, a hint and a full solution. New puzzle: Midnight Madrid time (the page says it is updated by the Europe/Madrid date).
Riddle of the Day publishes one logic or maths puzzle each day, chosen for a clear statement and a clean solution. You type your answer and check it, take a hint if you are stuck, and read a worked solution afterwards. Past riddles stay in an archive sorted by topic.
About Riddle of the Day
Riddle of the Day, also published in Spanish as Acertijo del día, is a daily puzzle page built by a mathematician trained at the Complutense University of Madrid; its structured data names Gabriel Sobrino as founder. Each day the front page shows one riddle with its date and a difficulty level out of five. The site's stated rules for a riddle are a clear statement with no hidden assumptions, a solution that can be defended without language tricks, and a difficulty that matches the level shown.
The riddles mix classics and less familiar problems: river crossings, knights and knaves, number puzzles and short thought experiments. You type your answer in an open box and press Check, which accepts answers in your own words rather than multiple choice. A Hint button and a Solution button sit under the box, and each riddle's own page explains the reasoning step by step, as in the eleven crossings of the missionaries and cannibals.
The site carries no ads and needs no account. A calendar and archive let you go back through earlier riddles by topic, a streak counts your days, and a share link sends a spoiler-free challenge. The same site also has a separate daily games page with small logic grids, listed on its own page here.
How to play Riddle of the Day
- Open acertijodeldia.com/en to see the day's riddle and its level.
- Read the statement carefully and work it out on paper.
- Type your answer in the box and press Check.
- If you are stuck, press Hint; when you are done, open Solution to read the full reasoning.
- Use the calendar or archive to try earlier riddles.
Screenshots
Tips
- Write down the constraints first: most riddles hinge on one condition that must hold at every step.
- Try small cases or work backwards from the goal.
- Take the hint before the solution: it usually points at the key idea without giving the answer away.
- The level shown (out of 5) is a fair guide to how long it will take.
Questions
When does the new riddle appear?
Each day by the date in Madrid; the front page shows the date it was updated for.
Is it free?
Yes, with no ads and no account needed. The site asks for voluntary support.
Can I play in Spanish?
Yes, the same riddles are published in Spanish as Acertijo del día; switch with the ES and EN buttons.
Can I see the answer?
Yes, each riddle has a Hint and a full worked Solution.
Ratings and reviews
No ratings yet. Be the first to rate Riddle of the Day.
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