Early Ryanair/Wizz/equivalent flight from Poznań to Paris; fastest cheap option to reach Paris and start sightseeing same day. Book early for lowest fares and carry-on only to save cost.
Low-cost shuttle from Beauvais to Paris center (~1–1.5h) or RER/bus if flying into Orly/CDG; necessary to reach city cheaply. Check shuttle schedules when booking (shuttle typically runs every 30–60 min).
Check into a budget private room or 4–8-bed hostel in central Paris (book advance for the best price); convenient base for walking to sights and public transport.
Visit Sainte-Chapelle (usually open 9:30am–6:00pm) and stroll the Seine/Île de la Cité to see Notre-Dame exterior; spectacular stained glass and an easy first-day walk.
Visit the Eiffel Tower (generally open daily; typical hours ~9:30am–11:45pm); book a timed ticket in advance to avoid long lines. Iconic view and a must-see on a short trip.
Musée d'Orsay is usually open Tuesday–Sunday (~9:30am–6:00pm) and houses world-class impressionist art — excellent alternative to Louvre on Tuesdays (Louvre closed Tuesdays).
Budget shuttle or public transport to catch the low-cost Paris → Prague flight; allow extra time for low-cost carriers' check-in rules (often earlier).
Walk up to Prague Castle complex (grounds often open early–late; St. Vitus Cathedral typical visiting hours ~9:00am–5:00pm) for historic architecture and superb views.
Morning walk on Charles Bridge and through Old Town Square to see the Astronomical Clock (free to watch the hourly show); best visited early to avoid big crowds.
If you need to return to Poznań on the 21st, FlixBus or similar operators run budget services (4–6h). Book early for lowest fares; otherwise end of itinerary in Prague.
Estimated total for flights, cheapest accommodation, local transport, food and a few paid sights for Poznań→Paris (2 nights)→Prague (1 night) between 18–21 Aug 2025. Prices fluctuate — this is an approximate planning number; I recommend booking flights and the Paris hostel ASAP to secure lowest fares.