聖壇 is read as せいだん (seidan) and means altar.
せいだん
seidan
せいしょ
Bible
せいじん
refined sake
せいじゃ
saint
せいぼ
mother of a holy person
せいち
real-life location used as a setting in a novel, film, anime, etc.
せいせん
holy war
せいいき
issue that is regarded as being off-limits
せいか
Olympic flame
せいしょくしゃ
clergyman
せいどう
(Confucian) temple
hymn
せいてん
writings of a sage