Napoleonica is about 20min drive from Trieste and very easily reachable by car. There's a big parking where the boulevard and the crags start from.
There's trails starting right from the parking which take you to the first sectors on the seaside of the boulevard. To get to the sectors above the boulevard, you can follow the GPS trail in these topos. There's also trails going straight up from the boulevard to these crags. When you want to get to the last sectors on the seaside, including Calabroni, just follow the boulevard until you're above them and look for a trail.
As the boulevard is popular not only among climbers, remember to respect everyone else enjoying this great place.