I still remember the first time when I saw videos about non-Euclidian Geometry[1] and Higher Dimensions[2]. I was amazed with such concepts, but I still havent read books about them. They are related somehow with topology[3] and curvature (and tangentially, to differential equations).
Also, a nice exercise to visualize 4D is to study quaternions and their properties. Vectors are somehow a nice simplification of them, see Maxwell laws. 3blue1brown has a video[4].
[1]https://youtu.be/n7GYYerlQWs (5 sided square)
[2]https://youtu.be/4TI1onWI_IM (The road to 4D part 1) https://youtu.be/N0WjV6MmCyM (Carl Sagan's explanation)
[3]https://youtu.be/lmcT2mP2bfE (Zach Star's intro)
Also, a nice exercise to visualize 4D is to study quaternions and their properties. Vectors are somehow a nice simplification of them, see Maxwell laws. 3blue1brown has a video[4].
[4] https://youtu.be/d4EgbgTm0Bg