On a budget, Giverny Day Trip (Monet's Garden) still earns its price.
€11 entry; €70–120 with guided transport
The garden that Monet painted obsessively, with the Japanese bridge and lily pond, is genuinely transporting in spring and summer. It's seasonal (closed in winter) and a real trek (~1 hr+ each way), but on a sunny day it's a highlight. Go early — it gets busy by midday.