Specifically a person who visits a temple, shrine, or similar religious/cultural site to view it, often with a respectful connotation from 拝観.
Many visitors come to this temple every year.
観光客 is a general tourist, while 拝観者 is specifically a visitor to a religious site for viewing purposes.
Compound of 拝観 (haikan, 'viewing with reverence, especially at a temple or shrine') + 者 (sha, 'person').