The archive comprises mainly correspondence addressed to Sir Walter and his first wife Pauline Lady Trevelyan nee Paulina Jermyn. The letters reflect the couple's interests in natural history, botany, geology, antiquities, travel, temperance, phrenology, art and literature, and include examples from many well known contemporaries.

There is also material relating to the history of the Trevelyan family, accumulated during Walter and Charles Edward Trevelyan's preparation of 'The Trevelyan Papers' for publication.

The archive also features diaries and journals, sketchbooks, notes for speeches and scrapbooks. There is material relating to the North East of England, including proposed railways, Tyne crossings at Hexham and decoration of the Great Hall at Wallington.

Describing travels in Italy, Elba, France, Scotland, the Netherlands and Germany, April 1837-July 1841. The file of loose material has been separated from the volumes and features sketches, notes, cuttings and correspondence. Correspondents include L Agassiz, Robert Bald, Charles Chalmers, John Graham Dalyell, David Douglas, Lord Eglington, D Robertson Macdonald, John Gibson Macvicar, Patrick Neill, and C Wilson.
For related correspondence see WCT/6/5 and WCT/6/6

Describing travels in the UK, Holland, France and Belgium, April 1862-Jul 1865. Also includes journal created at Neuchatel in 1866, recording the death of Lady Pauline. The file of loose material has been separated from the volumes and features receipt slips, pamphlets, correspondence and a copy of Lady Pauline's autopsy (French).

Describing travels in Italy, Switzerland, Greece, France, Scotland and Wales, March 1842-Nov 1844 The file of loose material has been separated from the volumes and features sketches, notes, cuttings, correspondence and printed ephemera. Correspondents include J Elliot, Philip H Howard, H Macdonald, George Oliver and James A Stothert.
For related correspondence see WCT/6/5, WCT/6/6 and WCT/6/7.