Since you arrive midday, use the morning for travel-light orientation and a relaxed start: stroll the leafy paths of Gellért Hill Park for elevated views of the Danube and a gentle introduction to Budapest's layout, then descend to explore the healing waters and historic Art Nouveau interior of Gellért Thermal Bath (book a short 90-minute session with lockers to refresh after travel). Finish with a late-morning gluten-free brunch at Cirkusz Cukrászda & Kávézó (they offer clear GF options and café seating) before checking into your Buda accommodation and preparing for the afternoon Castle District visit.
After freshening up, wander into the heart of the Castle District beginning with a relaxed walk along the historic cobbled terraces around Szentháromság tér (Holy Trinity Square) to admire the baroque facades and sweeping views of the Danube and Pest. Continue to the hilltop external grounds of Buda Castle for photo stops and then glide down the charming, traffic-free Fortuna Street toward Matthias Church's exterior and the panoramic Fisherman's Bastion terraces-pause at a café terrace offering gluten-free pastries while you soak in golden-hour light and plan an easy dinner in nearby Buda that keeps tonight mellow and accessible.
As dusk falls, take a gentle riverside stroll across the iconic Széchenyi Chain Bridge toward Pest for striking night views of the lit Castle District, then return to Buda to dine at Pest-Buda Bistro (ask for their clearly marked gluten-free menu items or the kitchen's GF adaptations). After dinner, enjoy a relaxed postprandial drink on the terrace of 21 Magyar Vendéglő or sip herbal tea at Kiosk Budapest's quieter corner, where low lighting and live piano on select nights create a warm close to your first day while staying within easy walking distance of your accommodation.
Begin with a wakeful stroll down the grand boulevards to Heroes' Square and the adjacent leafy expanse of City Park (Városliget), where you can admire monuments and rent a pedal boat or take a slow walk to the picturesque Vajdahunyad Castle exterior. From there, head to New York Café for a late-morning gluten-free brunch in one of the world's most opulent cafés (notify staff for GF options), then continue on foot to the striking domed Great Market Hall to sample local preserves, paprika shops and clearly labeled gluten-free sausages and snacks before crossing into the Jewish Quarter to begin your afternoon exploration.
After a morning in City Park and the Great Market Hall, head down grand Andrássy Avenue to Liszt Ferenc Square for a relaxed espresso at a café with clear gluten-free pastry options, then continue to explore the ornate exterior of St. Stephen's Basilica and climb the cupola for citywide views. From there wander into the historic Jewish Quarter to visit the evocative Dohány Street Synagogue and its moving Raoul Wallenberg Memorial Park, finishing with a guided tasting of gluten-free Hungarian specialties at a nearby kosher or GF-aware bistro in the quarter to connect history with contemporary local flavors.
As sunset settles over Pest, enjoy a leisurely riverfront walk along Rákóczi Terrace (Dunapart) toward the modern glass silhouette of Megyeri Bridge for unobstructed dusk views of the Parliament lights, then cross to the lively inner-city for dinner at Mazel Tov-a verdant courtyard restaurant in the Jewish Quarter with a clear gluten-free menu and creative Mediterranean dishes. After dinner, experience Budapest's contemporary cultural pulse with a cocktail at Doboz Ruin Bar (ask the bartender for GF mixers) or a short live-music set at the intimate Akvárium Klub to end the day with music, atmosphere, and easy walks back to your central accommodation.