For those not quite with British history, Oliver Cromwell was Lord Protector of England in the Commonwealth period after Charles I had been beheaded and before his son, Charles II, was restored to the throne.
The house is now used partly as a TIC, but the remaining part is particularly well arranged for school visits, etc. It shows something of the life of a rather puritanical family of the period, as well as providing a lot of information on Oliver, alive and dead.
He was buried in Westminster Abbey, but later his body was exhumed and the corpse was beheaded and stuck up for public view. It can hardly have been very recognisable!