Space, Time, and Gravity by Robert M. Wald or Gravitation by Charles W. Misner, Kip S. Thorne, and John Archibald Wheeler (the definitive, encyclopedic "MTW" text). Conclusion
Mattias Blennow, Tommy Ohlsson | Tensor | Special Relativity
The problems were collected and refined over two decades of teaching at the KTH Royal Institute of Technology. Space, Time, and Gravity by Robert M
The PDF version of the book is widely available online. However, I encourage you to verify the authenticity and legitimacy of the source, as copyright laws may apply.
Moving past basic algebraic formulas to solve advanced, multi-frame synchronization puzzles. However, I encourage you to verify the authenticity
General relativity (GR) extends the principles of SR to accelerating reference frames and introduces gravity as the curvature of spacetime. The math shifts from linear Lorentz transformations to non-linear differential geometry. Tensor Calculus and Differential Geometry
Resolving the Twin Paradox, the Ladder in the Barn Paradox, and the Spaceship Paradox using Minkowski spacetime diagrams. the Ladder in the Barn Paradox
Don't jump straight to the solutions! Try to struggle with the tensor indices for at least 20 minutes. That "struggle" is where the actual learning happens.