The original window of the tomb, which was a stained glass design, was vandalized many years ago. During renovation, this was replaced with a thick glass panel and this is the view you have if you climb the well-burnished metal rungs. Immediately beneath you is the altar, which is very hard to see. Notice the portraits of Isabel and Richard, fallen to the floor and inset in detail. This is likely a copy of the original that Louis Desanges presented to them  as a wedding gift (see below).
Inside the Tomb of Richard & Isabel Burton at St. Mary Magdalene's Church, Mortlake, London
Louis Desanges' wedding portraits of the Burtons (1861)
Here (below) you see Burton's gilded metal coffin with the now-legendary "camel bells" lying on it  The white object projecting upwards at the right is the vertical of a large crucifix on the altar, its horizontal broken
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I wonder if you agree with my opinion that  Desanges' treatment of Richard here is noticably more sensitive than  that of Isabel?
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Although the exterior of the tomb was refurbished in 1974, the inside was left without any renovation; perhaps some cleaning was done and objects catalogued but nothing beyond that.  It has endured remarkably well.
From: Burton Collection, Richmond Borough Art Collection. Reproduced by kind permission of Orleans House Gallery