In the late 1990s, I took my mother to Italy on her first trip overseas since study abroad in Perugia, more than three decades earlier.

A lot had changed. Mom was saddened by the modern sprawl that had mushroomed around historic city centers. She was tickled by the sight of fashionable young men chattering into “telefonini,” fake cellphones with the singular aim of impressing nearby females.

But what shocked Mom the most, without a doubt, were the crowds. Everywhere we went, hundreds more tourists went with us, alongside polyglot recent arrivals from Africa, the Middle East and beyond.

There were lines to enter Madrid’s Royal Palace, lines to see the Botticellis at the Uffizi, and so many trinket merchants on the Ponte Vecchio that it was hard to see the Arno.

Twenty years later, the crowds have multiplied exponentially. Where once you needed advance tickets to avoid standing in line at big-name sights across the U.S., Europe and beyond, now you’ll often need them to enter at all — and you may have to make those reservations months in advance.

As you plan this summer’s travel, consider this: Spontaneous travel is still possible, but it’s more restricted than it used to be. If you’re not willing to spend many precious (and hot) hours standing in line or forego must-see sights for those off the beaten track, then planning is essential.

I admit to nostalgia for the days when I would book a flight on a few days’ notice to Paris and decide I was in the mood to check out the Louvre, or the Eiffel Tower — and then just simply show up.

Today, lines for both places rival the queues I recall from winter vacation week at Disney World (a ride signpost reading “Approximate wait time from this point, 2.5 hours” is my most indelible memory, decades later).

To avoid frustration, here’s my tip: Think the way you would at home. How do you avoid crowds at Trader Joe’s? At the hot new restaurant? On the subway? By going at off days and hours, avoiding promotions and, where possible, booking a slot in advance.

I routinely dine at the unfashionable hour of 5 p.m. on Sundays, enjoying the relaxed feel of off-peak dining. In the same spirit, I visit the most popular European museums midweek, in the dead of winter, or very late in the day; in cruise ports of call, I arrive early, before the ships dock.

Have you ever noticed how sparse the crowds are at Trader Joe’s and Ikea on Friday and Saturday nights, when most locals are out doing something more exciting? It works the same way at many museums during their special evening hours, when tourists are either dining or tucked into bed.

The courtyard of the Louvre museum in Paris. Wikimedia Commons

A while back, I decided life was too short to stand in line for food. I eschew Restaurant Week and other such specials, figuring my time is more valuable than whatever money I’ve saved.

I take the same approach overseas; after a full morning camping out for the Prado’s free-entrance day, I decided I vastly prefer to pay full price at a less-congested time.

Check in advance to make sure your visit doesn’t coincide with a local holiday or a day when most other sights are closed, when crowds typically double. Then make timed online reservations for your can’t-miss list of eateries, castles and art exhibitions, allowing you to skip the line.

Many popular cities sell multi-site tickets for their top attractions; entry passes are often also available at visitor kiosks, tourism offices and other local venues, for those who can’t commit before arriving in town. Alternatively, guided tours often include entry to the most-coveted destinations — and since they’ve reserved blocks of tickets in advance, it can often get you into a sold-out museum at the last minute.

As any synagogue tourist will know, advance confirmation is often absolutely essential if you hope to tour a temple, enjoy Shabbat hospitality, or visit a Jewish site. This is often more about security than crowding, but the rule is the same: Plan ahead, bring multiple documents and confirm once again — or be disappointed.

Every year, I’m amazed by crowds of people in places where there never used to be crowds, even in towns that used to be relatively out-of-the-way (travel guru Rick Steves’ so-called “back door” villages, like the Cinque Terre, are notorious for this). It’s an irony of our modern age that the sights most affected are those we visit precisely for their timelessness.

But what we sacrifice in spontaneity, we gain in convenience — so reserve at leisure, and then relax once you arrive.