A fabulous, inexpensive lunch spot atop tombstones in the crypt of St. Martin-in-the-Fields church on Trafalgar Square
Do not buy point-to-point tickets. What you want is an Oyster Card (possibly with a Travelcard transit pass).
Henry Liddell, the Dean of Christ Church College from the 1850s to 1891, had a duaghter in 1852 he named Alice Pleasance Liddell. The Liddell family struck up a friendship with a mathematics professor named Charles Dodgson, who would regale the Liddell sisters with elaborate fantasy tales on their boating trips down Oxford's rivers. Little Alice begged Dodgson to write some of them down, and he did, using the pename Lewis Carroll, casting a precocious seven-year old girl named "Allice" as the protagonist, and eventually publishing Alice in Wonderland and Through The Looking Glass and What Alice Found There.