You'll only want to go to Northampton once..................there's not a lot there to recommend making a second visit. Bit like Luton really!
Some recommendations:
The Guild Hall - Ruskinian Gothic at its finest, the masterwork of E W Godwin
78 Derngate - complete Charles Rennie Macintosh interior
Royal Theatre - Edwardian interior
Museum & Art Gallery - boasting an extraordinary collection of boots and shoes
All Saints - few finer late 17th-century churches outside London (the poet John Clare spent much time under its portico)
St Peter's - fine, completely Norman, church
Holy Sepulchre - a rare round church, one of only four in England
St Matthew's - Victorian church with 20th-century art ("Madonna" by Henry Moore, "Crucifixion" by Graham Sutherland)
St Giles' - grave of Robert Browne, "father" of the independent / congregationalist Puritans
And, in the cemetery at the bottom of my street can be found the graves of Lucia Joyce (James Joyce's daughter) and Violet Gibson (the woman who shot Mussolini). The finest Bloomsday outside Dublin.
Now, what has Luton got to offer?