All of London's history and development is linked with the River Thames: This winding ribbon of water connects the city with the sea, from which London first drew its wealth and power. The Thames was London's chief commercial thoroughfare and royal highway. Every royal procession was undertaken on gorgeously painted and gilded barges (which you can still see at the National Maritime Museum in Greenwich). Important state prisoners were delivered to the Tower of London by water, eliminating the chance of an ambush in one of the narrow, crooked alleys surrounding the fortress. Much commercial traffic on the water disappeared when London's streets were widened enough for horse-drawn coaches to maintain a decent pace.

River Cruises Along the Thames -- A trip up or down the river will give you an entirely different view of London than the one you get from land. You'll see how the city grew along and around the Thames and how many of its landmarks turn their faces toward the water. Several companies operate motor launches from the Westminster piers (Tube: Westminster), offering panoramic views of one of Europe's most historic waterways en route.

Westminster-Greenwich Thames Passenger Boat Service, Westminster Pier, Victoria Embankment, SW1 (tel. 020/7930-4097), concerns itself with downriver traffic from Westminster Pier to such destinations as Greenwich (see "Attractions on the Outskirts," below). The most popular excursion departs for Greenwich (a 50-min. ride) at half-hour intervals between 10am and 4pm April through October, between 10:30am and 6pm June through August, and from 10am to 3:20pm November through March. One-way fares are £6.30 ($10) for adults, £3.90 ($6.25) for children under 16, £5.20 ($8.30) for seniors. Round-trip fares are £7.80 ($12) for adults, £3.90 ($6.25) for children, £6.30 ($10) for seniors. A family ticket for two adults and up to three children under 15 costs £16.80 ($27) one-way, £20 ($32) round-trip.

Westminster Passenger Association (Upriver) Ltd., Westminster Pier, Victoria Embankment, SW1 (tel. 020/7930-2062 or 020/7930-4721), offers the only riverboat service upstream from Westminster Bridge to Kew, Richmond, and Hampton Court. There are daily sailings from the Monday before Easter until the end of October on traditional riverboats, all with licensed bars. Trip time can be as little as 1 1/2 hours to Kew and between 2 1/2 to 4 hours to Hampton Court, depending on the tide. Cruises from Westminster Pier to Hampton Court via Kew Gardens leave daily at 11 and 11:15am, and noon. Round-trip tickets are £12 to £18 ($19-$29) adults, £9 to £12 ($14-$19) seniors, and £6 to £9 ($9.60-$14) children 4 to 14; one child under 4 accompanied by an adult goes free.

Exploring London's Canals By Boat -- Boat trips on London's canals, especially Regent's Canal in London's canal-laced "Little Venice," are becoming an increasingly popular way of seeing the city. Bus no. 214 takes you to Little Venice, where you can board one of several boats for a tour along the canals. You can return either by boat or by Tube from the nearby Underground station at the end of a one-way trip.

Since the Festival of Britain in 1951, some of the traditional painted canal boats have been resurrected for Venetian-style trips through the waterways. One of them is Jason, which takes you on a 90-minute trip from Bloomfield Road in Little Venice through the long Maida Hill tunnel under Edgware Road, through Regent's Park, past the Mosque, the London Zoo, Lord Snowdon's Aviary, and the Pirate's Castle, to Camden Lock, and finally back to Little Venice. Passengers making the 45-minute one-way journey disembark at Camden Lock.

The season runs from April through October, with daily trips at 10:30am, and 12:30 and 2:30pm. In June, July, and August, an additional trip on weekends and bank holidays leaves at 4:30pm. A canalside seafood specialty restaurant/cafe at Jason's mooring offers lunches, dinners, and teas, all freshly made. Advance notice must be made for lunch service on the boat. The round-trip fare is £6.95 ($11) for adults and £5.50 ($8.80) for children and seniors. One-way fares are £5.95 ($9.50) for adults and £4.75 ($7.60) for children and seniors. Family tickets cost £20 ($32). For reservations, contact Jason's Trip, Jason's Wharf, opposite 60 Bloomfield Rd., Little Venice, London W9 (tel. 020/7286-3428; Tube: Warwick Avenue).