My party will be going to a temple soon, and I'm wondering if a vampire (who is stalking them unbeknownst to the party) will be able to enter. It's to an evil god, but the ground is still technically hallowed so I'm wondering if the creature would be able to even get into the temple grounds let alone the temple.
The template lists all weaknesses of Vampires:
Weaknesses: Vampires cannot tolerate the strong odor of garlic and will not enter an area laced with it. Similarly, they recoil from mirrors or strongly presented holy symbols. These things don't harm the vampire—they merely keep it at bay. A recoiling vampire must stay at least 5 feet away from the mirror or holy symbol and cannot touch or make melee attacks against that creature. Holding a vampire at bay takes a standard action. After 1 round, a vampire can overcome its revulsion of the object and function normally each round it makes a DC 25 Will save.
Vampires cannot enter a private home or dwelling unless invited in by someone with the authority to do so.
[...] (exposure) to direct sunlight, [...] immersion in running water, [...] wooden stake through [the] heart [...]
Assuming your temple is not laced with garlic and is not a private home (or inside a private home), the most troublesome part are holy symbols.
Seeing that it takes a standard action to repel a vampire using a holy symbol, "strongly presented" seems to refer solely to characters or NPCs "strongly presenting" their holy symbol, as in the description of Channel Energy:
A cleric must be able to present her holy symbol to use this ability.
Arguably though, holy symbols in a temple are "strongly presented", they are usually central to the whole design (think of crosses in christian churches).
(Personally, I'd rule the latter case, because I don't like the idea of vampires walking in the front door of a Sarenrae temple, but commoner with a carved holy symbol can repel him...)
In any case, the weakness does not pertain to unholy symbols, so your bad guy is good to go.
Typical area spells found in evil temples of doom also don't hinder vampires. In fact, a vampire benefits from desecrate the same way all undead do. Unhallow also has no special effect that prevents a vampire from entering. As Jeor Mattan points out, not even hallow can prevent Vampires from walking in the front door.
In the vampire template, there is a section called "weaknesses", that describes the following restrictions to a vampire's abilities:
- Held at bay by strong garlic odor, mirrors and strongly presented holy symbols.
- Cannot enter a private home or dwelling without invitation.
- A stake through the heart kills it.
Number 3 is pretty irrelevant to the situation, so we can ignore it. Number 2 however, could be problematic. In general, temples and churches are considered public places, and a vampire wouldn't normally require an invitation to enter. If the temple no longer functions as such and is used as a permanent hideout by someone, though, then the vampire would require an invitation.
Assuming your temple is a public place, number 1 shouldn't be so problematic. The rules require a wielder for the holy symbols, as they must be strongly presented. As long as the vampire can keep his nature hidden (no display of vampire powers, no eating people in public, etc.), no one should be bothering him.
You also indicate that this would be an evil temple. as such, the ground wouldn't be hallowed, but unhallowed. This would mean that a vampire in this temple would have a harder time resisting the channel energy effects of an evil cleric or a neutral one channeling negative energy, which would normally heal him (and there's no reason he wouldn't thus willingly fail his save). He would also be stronger against good clerics and neutral ones who channel positive energy, reducing the DC of the saves to resist such effects by 4.
- There's no reason he shouldn't enter if the temple is still used as a public gathering place for the followers of the worshiped god.
- Unless someone strongly presents a holy symbol, a mirror or the place is drenched in garlic, the vampire should have no issues inside.
- If it's a temple to an evil god, the vampire would in fact be stronger against good aligned channel energy.
As written, there's little that prevents a vampire from entering.
Hallow effect technically does not ward either undead nor evil creatures that are native to the plane of existence on which the effect is situated. The standard list of effects that could be attached to the hallowed area does not help that issue, either.
Furthermore, the temple is not a private dwelling, so the vampire can enter it uninvited.
Even holy symbols require a living operator (emhpasis mine):
Similarly, they recoil from mirrors or strongly presented holy symbols. These things don't harm the vampire — they merely keep it at bay. A recoiling vampire must stay at least 5 feet away from the mirror or holy symbol and cannot touch or make melee attacks against that creature. Holding a vampire at bay takes a standard action.
So, technically, it can enter freely.