Click on Mathigon to start exploring. Check out the activities and puzzles. This is a great place to learn something new through exploration.
Check out Dr. Raj Shah's Youtube Channel. He poses new math challenges each week. He calls them his Math Treats. See if you can conquer one of his many challenges. Share your findings on your classroom Seesaw.
Check out Steve Wyborney's site. You may want to explore his Esti-mysteries or play a few rounds of Splat. After exploring, you can share something on Seesaw or just share it in class. Enjoy!
Visit Graham Fletcher or Dan Meyer's site to explore 3 Act Math Tasks. There are many tasks for every level. Try one from your grade level or give yourself a challenge and find one from the grade level above. You can share your findings on Seesaw or with your classroom. Let us know what you have discovered.
Visit the Greg Tang math site. You will find a variety of math games to play online. Greg Tang is the author of many math books. You might know a few of them from school.