Hi, I think that no one mentioned the books by Marcos Mateu-Mestre, Framed Perspective Volumes 1 and 2. They are full of drawing demonstrations and work as an excellent companion for How to Draw (by SR). You could use the demonstrations by Marcos as assignments. 

I will start today in drawabox.com, it looks pretty cool. Marshall 1994 course is a one wonder gem haha

Scott Robertson's books?

Draw a box is exercise-heavy and has a strong emphasis on perspective and structure. Its exercise can be more tedious than fun per se. ArtWOD is almost entirely exercising; they do a class session, but typically, it's gear around exercises, but it is a great way to learn structure and perspective without learning perspective. Other than that, Bookwise. Perspective Made Easy by Ernest R. Norling & Perspective Drawing Handbook by Joesph D'Amelio. In my experience, all dedicated perspective courses/books typically cover the gamut; so it's up to you to know when to walk away.

Erik olson!

Have you looked around at @Irshad Karim ’s Draw A Box? I haven’t done it, but I hear good things from other members here - it might be worth taking a look around. Good luck ☺️.

@Trancematica Off the top of my head, I can't remember a good and fun course on perspective that includes assignments, sorry. I'm still waiting for @Marshall Vandruff's perspective course on Proko to fill in this gap :D But I do have some "consolation" recommendations. Personally, I'm a fan of the tutorials on CtrlPaint, and they have a paid series about perspective that I watched a few years ago and that were a huge help for at the time. Unfortunately, it doesn't include assignments either, but it's very practice-oriented, so you might intuitively figure out how to apply the ideas directly into drawing studies or personal projects (ah, it's also targeted towards digital drawing in Photoshop by the way - not sure if this is an advantage or a disadvantage to you). But overall, in my opinion, the highlight of this series is that it brings a view of perspective that makes it easier for beginners to get - it explores a lot of using a perspective grid instead of placing vanishing points "from scratch" on the drawing page, and at least for me, this helped deal with constructing scenes in perspective in a whole new way. So, if you'd like to check it out: https://ctrlpaint.myshopify.com/collections/foundation-skills/products/perspective-sketching-1-the-basics Also, there's the book "Perspective made easy", by Ernest Norling, which I haven't read, but a lot of people seem to love. Not sure if it contains assignments though. And, while Marshall's course on Proko won't come out, I can't recommend enough his 1994 perspective lectures. But since it has no assignments, one thing I did when I watched them a while back was to make a lot of notes for myself - I'd basically pause each video a bunch of times and make diagrams of all his explanations, and I felt this helped me almost as much as a real assignment. Have you tried it?

Hello! The next best thing to self learning (and the laziness issues that come with studying fundamentals) would be to take a class! Brainstorm School and Concept Design Academy have Perspective Boot Camps/ dynamic drawing classes if that would interest you. But another issue you brought up was the simplicity and fun in drawing! There's no way around the work that has to be put into it, but something that might help you study perspective is applying it to what you like to draw already. That way you might enjoy the process a little more and you won't need to draw perfect cubes in space to start getting the hang of it!