What does the cryptic crossword clue "Sad Peter inside ground made accessible for walking? (14)" mean?

The wordplay uses an anagram. anagram of SAD + PETER + INSIDE = PEDESTRIANISED The answer is PEDESTRIANISED.

Sad Peter inside ground made accessible for walking? (14)

Daily Mail Cryptic #17307 | 26 Across | 2024-03-05 flower