The Altar is a custom Pokemon-Planet feature and is located in Vermillion City.
When the target of $4,000,000 is reached, double experience will be applied to the entire server for 1 hour. To check if the Altar is in use, look in the top-left corner.
There are 3 altars: Arceus, Kyogre and Diancie. These double pokemon exp gain, fishing exp gain and mining exp gain respectively.
Money or Credits can be donated to reach the target. You can check how much money has been donated by typing /altar in chat.
Donating 1 credit converts to $2,000
For every $800 donated, you will receive 1 Philanthropist Point (rounded down).