Albergo del Senato is a great little place. It is right on the same piazza as the Pantheon and has a really nice roof top bar. We love it there but it is pretty small and very popular so I would suggest you book as soon as you know your dates.
our other fave hotel in Rome is the Intercontinental at the Spanish Steps. Very nice , bigger than the Senato and usually way more expensive. The location is fantastic at the top of the Steps, next door to the Hassler.
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Helen