Sanctum Spell( Complete Arcane, p. 82)
Your spells are especially potent on home ground.
Any metamagic feat,
A sanctum spell has an effective spell level 1 higher than its normal level if cast in your sanctum (see below), but if not cast in the sanctum, the spell has an effective spell level 1 lower than normal. All effects dependent on spell level (including save DCs) are calculated according to the adjusted level. A sanctum spell uses a spell slot of the spell's normal level.
Your sanctum is a particular site, building, or structure previously designated by you, and no larger than 20 feet/level in diameter. The designated area must be a site where you have spent a cumulative period of at least three months. Though a sanctum can be designated within a larger structure, its special advantages do not apply beyond the maximum area. Once designated, it takes seven days for a site to become a sanctum, and if you designate a new area to be your sanctum, the benefits of the old one immediately fade..