Sky Garden (Sky Pod Bar)

Perched on the top floors of 20 Fenchurch Street, Sky Garden is the rare rooftop that costs nothing to enter — booking a free timed slot online is strongly recommended — released weekly on Mondays roughly three weeks ahead, so weekend and sunset slots vanish within minutes — though limited walk-ins are sometimes available subject to capacity. The lush, terraced indoor garden opens onto an outdoor terrace with near-360-degree views taking in The Shard, Tower Bridge and the river below. The Sky Pod Bar sits among the planting and serves cocktails, wine and small plates from around midday. A useful trick: if the free garden tickets have gone, you can book a table directly at the bar or a restaurant (bookable up to about 60 days ahead), which guarantees entry and a seat — worth it for sunset, when the standing bar can't promise a window spot. It pairs a genuine showstopper view with free entry and easy access, which is why it tops our list.