For a first Europe trip this is ambitious, but not totally unhinged.
The Belgium + Tomorrowland block makes sense since the festival eats a big chunk anyway. Ghent and Antwerp are great calls for day trips, honestly nicer than Brussels itself. One day in Brussels is plenty.
Netherlands wise, 4 days Amsterdam is solid. For the extra 2 days, I’d look at Utrecht or Rotterdam. Utrecht especially fits your vibe if you like food, running, and pretty scenery without tourist overload.
Paris for 5 days is great. For the extra 2 days nearby, somewhere like Lyon makes a lot of sense for a foodie, or even Strasbourg if you want something very different without going far.
London 6 days is fine, especially if you like neighborhoods, food, and long walks or runs. You won’t be bored.
Madrid + San Sebastián is a great combo, just be aware it’s a bit of travel for only 5 days total. San Sebastián is absolutely worth it for food alone though, so I get why it’s on your list.
Italy is the only part that feels tight. Rome deserves 3 days minimum, but I’d strongly lean Florence or Bologna over Amalfi or Cinque Terre given your interests and the time of year. No car needed, amazing food, history everywhere, and way less logistical pain.
Trains are the right call almost everywhere you listed. July and August flights can be cheaper sometimes, but the time suck usually isn’t worth it unless the distance is big.
Overall, it’s fast paced, but for a first Europe trip with lots of cities, food, and culture, this actually makes sense. Just expect to be tired and build in a couple slower days where you don’t move cities.
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