Once you reach Lv 75 in DBZ Online, Ancient Ruins will be available to you for exploring. While exploring ancient ruins, you have to fight enemies on each floor. After you win, you will be rewarded with corresponding spar item. Spars are used to enchant your gear even further. You can read about enchantment here
Each ruins have 30 floors and new ruins is available to explore after your level reach certain Level.
Every day can only choose 1 Ancient Ruins 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.