The oldest travel guide to Belize that I've been able to find is the brief, seven-page chapter on British Honduras in The Pocket Guide to the West Indies
by Algernon Aspinall (later Sir Algernon Aspinall.) It was first published in 1907, in London. The edition I have is from 1923 (earliest editions are collectors' items that I can't afford). The original 1907 edition (now out of copyright) is available in pdf and other formats at http://openlibrary.org/books/OL6987761M/The_pocket_guide_to_the_West_Indies
-- the 1907 edition does not cover British Honduras.
This 479-page guide (plus there are several pages of advertisements as an appendix) that I have covers most of the Caribbean, along with the Bahamas, Bermuda, British Guiana (sic) and British Honduras, the Spanish Main and the Panama Canal.
Information on British Honduras is very limited, but Aspinall does note that lodging in Belize City is available at "Mrs. Macdonalds and Miss Stanier's lodging in Regent Street. Board and lodging $1.50 per day and upwards."
Of Belize (City)
"Belize (population 10,478), the capital and seat of government, is approached from the open sea by a tortuous channel through the numerous reefs and cays lying off the coast, prominent among which are Turneffe, St. George's Cay, English Cay and Ambergris Cay. It has been said by the irreverent that the best view of Belize is obtained from the stern of a ship. The first appearance of the town with its white and red roofed houses rising from the sea is quite pleasing. A large white building to the left must not be mistaken for a hotel which it much resembles; it is St. John's College, a Roman Catholic Institution conducted by American Jesuits, about a mile from the town. On a clear day the great mountains of the interior can be seen in the dim distance...The principal thoroughfare is Regent Street, at the end of which are (left) the spacious Government House with a lawn running down to the sea, and (right) the old Cathedral church, erected in 1810. Conspicuous alongside the tower is a large water vat, which serves as a reminder that the town is dependent on rain for its supply of drinking water. The street is quite innocent of paving and is honeycombed by the holes of land crabs which dart back into them as you approach...Along the river fronts are stores and private residences. A bridge connects two parts of the town, and the river below presents a busy scene with its numerous pitpans -- the native boat -- and motor-boats, which ply between the capital and El Cayo, 100 miles distant on the western frontier, where goods are transferred to mule-back for the Peten district of Guatemala, the cays, the rivers, and various points along the coast."
Of other attractions,
"Sergeant's Cay, Goff's Caye, English Cay, and Tobacco Caye, are a few of the numerous cayes lying along the Coral reef about ten miles to windward of the mainland which, occasionally resorted to by visitors who are satisfied with sea-bathing, fishing, and sailing...
"Manatee, some fifteen miles to the south of Belize, is another holiday resort of rather a primitive character. Here there are extensive lagoons. At Ben Lomond, on the Northern Lagoon there are stalactitic caves...
"On the Rio Grande in the Stann Creek District some ancient pyramids faced with cut stone, filled with stone and brick and standing on a stone-faced platform, are preserved as historic monuments. Their origin is unknown. In the Cayo District, near Benque Viejo, there are also some interesting ruins."
in British Honduras, Aspinall writes:
"Lawn-tennis is played on concrete courts of the polo and golf clubs, and there are also several private courts. Cricket is played from May to October, and there are several native cricket and football clubs. The Belize Golf Club, which was established in 1900, has a nine-hole course (subscription $1.25 per month and $10 entrance fee.) Polo is played on Tuesdays, Thursdays, and Saturdays from October to March by members of the Belize Polo Club founded in 1895 (subscription $15 per annum and $7.50 entrance fee)...Fishing is a pursuit which is not much followed, though tarpon, calipever, snapper, bass, mullet, grouper, king-fish, and barracouta are plentiful."
"A Government railway runs inland from Stann Creek to Middlesex, a distance of 25 miles. The roads are not at present suitable for wheeled traffic except in the immediate vicinity of towns, and between El Cayo and Benque Viejo."