N 48° 13.775
E 16° 24.544
As you are standing at the coordinates of stage 1 you will discover a construction which is quite unusual in a city but not so unusual at a coastline. Count all doors of the constuction which are not made of glass. The result is L.
N 48° 13.003 + (L*50)
E 16° 24.817 + (L*L*10)
Based on the final coordinates of stage 2 you can calculate the next stage. You will find all information you need at this place. Just look around...
The Neptune with his trident is already waiting for you. But, he won't give you a hint. The only thing you can get from him is a 2-digit (A) and a 3-digit number (B) seperated by a dash.
N (Stage 3N result) +(A/2) +1
E (Stage 3E result) -(B*3) +13
So you finally reached the cache location. It was not that difficult, was it? You are just right when you cannot see the promenade anymore. The cache contains inline skating related stuff.