Experiments you can run yourself.
Moving clocks run slow: Δt=γ·Δt₀, where γ=1/√(1−v²/c²). The effect becomes noticeable only at speeds close to c.
A moving object is shorter along the direction of motion: L=L₀/γ. The dimension transverse to the motion does not change. Always L ≤ L₀.
Total energy E=γmc², rest energy E₀=mc². As v→c, the energy grows to infinity — that is why the speed of light cannot be reached.
A twin travelling near c comes back younger than their twin.
The sum of two velocities close to c never exceeds c.
The interferometer detects no "ether wind" — the speed of light is always the same (Nobel 1907).