The archives, manuscripts and printed books detailed in the online databases here are held in many different locations throughout Europe.
Some institutions are dedicated archives or libraries with full time professional staff and facilities; others function primarily as educational or administrative institutions which do not have staff or resources to deal with unstructured enquiries or unannounced visitors.
This website provides full details regarding each of the institutions, how to contact them, what facilities are available, and what their holdings are.
If you wish to consult any items or request copies, this must be made in writing to the institution which holds the material (the Catholic Heritage project does not hold copies of any material).
If planning a research trip, you should make a request by email or in writing, with advance notice, to the institution with full details of intended research, and an estimation of when you might be able to visit.
In the case of seminaries in Europe, this often requires up to six months notice because the archives and libraries are staffed by visiting staff from the United Kingdom who assist institutional staff with requests and are only available at certain times of the year.