Bourgas definitely isn't in the same league regarding beaches as its close neighbours of Sozopol, Nessebar, Sunny Beach and etc. but it does have quite a reasonable stretch of sand in front of the Sea Gardens. The dark-coloured sand looks as if it is dirty but in fact the discolouration is merely due to naturally-occurring minerals and is actually reputed to have curative powers.
There are two adjacent beaches, the Old Beach and the Central Beach, divided by "The Bridge" (which is in fact a pier) and by all accounts they are very popular in the summer with locals and visitors alike and are fronted by a variety of cafes and bars. Unfortunately I was here on a windswept May afternoon and so the beaches were all but deserted and (more unfortunately!) the cafes and bars hadn't opened up yet for the season but The Bridge was still quite popular as a local promenade.
One of the best city beaches I've been to, it streches for 2-3 km along the Sea Park, it's close to the centre so you can walk there, close to the main train and bus stations, it's relatively clean, with lifeguards, many cafes and restaurants, even small stalls with beach stuff, there are less tourists and it's free (only the part next to the port is paid, I think, anyway, it's not the best part). My favourite is what they call the Old Beach, it's in the north part. Anyway, that's the one closest to my parents' place. There is beach volleyball, a wind-surfing club and many small restaurants. In the summer of 2004 we had great great weather, it stayed pretty warm till the beginning of November. The last day we went to the beach was November 1st! The sea was still warm enough for me and I swam ( I wasn''t the only one, though). Last summer (2005) unfortunately there were many rainy and cold days and the last time we went to the beach was in the beginning of October.