On 5th April 2025, I made my jump from the Old Bridge of Mostar. Here is the guide for people who are also considering doing it to keep the five-century-old culture alive.
Many people died jumping off the Old Bridge, and many got permanent injuries — not even mentioning the ones with temporary injuries, the ones who open their eyes in a hospital. So you go to the diving club on the bridge to get proper training. They will also keep their people down to make sure if you mess it up, you can be taken out of the water properly rather than having an unconscious travel to Croatia.
There are three training platforms with different heights: 7 m, 12 m, 17 m (may slightly change depending on the water level). True beginners start with 7 m, and the closest jump to the Old Bridge jump is 17 m. The trainer will give you feedback after you jump, and they will let you jump when they think you are ready.
Hit the water, don't let it hit you is the main thing for a good jump. Before you enter the water, bend the knees a little bit and do it straight (as if you are kicking the water) before you enter the river.
Training Jump - 17m
Another Training Jump - 17m
After 6 training jumps (2 from 12m, 4 from 17m), you are ready to go for the Old Bridge jump (23m ± 2m).
After a successful jump, you are given a certificate from the diving club, with a rank showing your order from the people who officially jumped since 2004; mine was 4357.

And your name is recorded in the book of divers, with your signature, just like other people who made successful jumps.