The following are great sites that I personally recommend to learn from. You can click on the images to be linked to the site.

An interesting site completely devoted to time. They discuss mathematical, physical, and philosophical interpretations both modern and historically. Various experiments as well as proposed time travel devices are mentioned. Altogether, a very fun site.
Mandel Bulb is an amazing site that consists of the work of various artists who make works out of 3D fractals. The work above is a real mathematical fractal. Check out some of their other works.
MinuteLabs is a site filled with fun simulations, interactive graphics, and other nice things to just experiment with and look at.
A collection of pages called “Cantor’s attic” covers information about all types of infinity, large numbers, and other crazy topics in transfinite set theory. It is still in development but provides an amazing and vast collection of various types of ordinals and cardinals and concepts about axioms and such.
A blog called “Quantum Diaries” written by physicists through international collaboration which explains various phenomena in particle physics, quantum mechanics, and some cosmology.
A collection of online courses created by MIT and Harvard but includes lessons by professors all over the world. I personally recommend taking the Cosmology which is a great introduction into General Relativity.
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A YouTube Channel called “3Blue1Brown” that teaches really complex and interesting math through elegant visualizations.
A very popular site that frequently posts science articles in all disciplines discussing very current technology and science being developed.
A YouTube channel called “NumberPhile” where an immense amount of interesting concepts in mathematics is explained in very simple ways.
An online source to read all the Feynmann lectures which covers various topics in physics (mechanics, electromagnetism, quantum mechanics) and is a great source for learning complex concepts in a simple manner.