It is possible to book at least the restaurant for a lunch even not being your hotel client since it looks impossible to book a room?
All the best
There were always some guests from outside during lunch or dinner time. It should also be possible to reserve a table beforehand, since especially for dinner is strongly recommended.
I'm sure it is although we did not have to do that. We arrived midday and had our choice of seating.
Get an answer from Belmond Hotel Splendido staff and past guests.