Once you reach Lv 75 in DBZ Online, Ancient Ruins will be available for you to explore. While exploring ancient ruins, you have to fight enemies on each floor. After you win, you will be rewarded with corresponding spar items. Spars are used to enhance your gears even further. You can read about enhancement here.
Each ruins have 30 floors and new ruin is available to explore after your level reaches certain Level.
Every day can choose only 1 Ancient Ruin to explore. Also you can only lose 3 times and then the exploration stopped. Unlike trials though, you won't immediately go to you last floor but start from 1st floor again if you choose to explore same ruins on the next day.