The Jeronimos Monastery is one of the finest examples of Manueline architecture. It is lovely and fanciful--and the carving surrounding every window is unique. Each craftsman was allowed the freedom to customize his window. But you need to look closely to see that! The overall impression is of the carved rope motif so common in Manueline architecture.
On a recent visit to the monastery, in addition to enjoying the serenity of the cathedral and the astonishing size (and incredible tile pictures) of the refectory where the monks ate their meals, I was delighted to discover that there was a concert being conducted in the cloister. What a joy to sit comfortably and listen to the choir serenade us all, for free. (Well, no additional charge, anyway.)
The monastery is across the street and a park from the Monument to the Discoveries, and within easy walking distance of the Tower of Belem. It is easy to reach Belem to visit the monastery, the Tower of Belem, and the Monument to the Discoveries. It is a short and inexpensive cab ride from the riverside in downtown Lisbon, and there are also frequent trams. To return, there is a cab stand directly across the street form the monastery.